Manila, Philippines (CNN) Philippine officials are appealing to residents not to return to their homes in the danger zone of an erupting volcano as it continues to spew plumes of ash and lava fountains, with earthquakes regularly shaking the ground.

As of Tuesday, almost 20,000 people from Batangas and Cavite provinces have sought shelter in 118 temporary evacuation centers set up by authorities. The total number of evacuees is likely to be higher, with some choosing to stay with family members and relatives in other parts of the country.

Officials, however, said a number of residents were beginning to return to their homes close to the volcano to tend farms, livestock or fetch personal belongings.

A resident cleans the roof of their house filled with ash spewed by Taal volcano in Tagaytay city.

Many people depend on the lake and land around the volcano for their livelihood. Their dilemma is whether to risk their lives by returning or their primary sources of income by staying in a shelter for an unknown period of time.

"If you were this person and think 'well all I know for sure is I have three cows, seven goats and some soy beans and I don't go back and take care of them, I know I'm screwed,' than someone telling you to stay away for two weeks and maybe nothing happens -- you're in trouble anyway," said Joseph Michalski, director of the Earth and Planetary Science division at the University of Hong Kong.

There are two concentric zones of concern around the volcano. Around 459,000 people reside within a dangerous zone within a 14-kilometer (8.6 miles) radius around the volcano, according to the United Nations Office for the Coordination of Humanitarian Affairs (OCHA), while more than 930,000 people live in a wider 17-kilometer (10.5 miles) danger zone.

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) has requested a "total evacuation" of everyone within the larger 17-kilometer (10.5 miles) radius around the volcano.

Mariton Bornas, chief of volcano monitoring and eruption at PHIVOLCS said residents within the immediate radius would be at risk of tremors, fissures and the threat of a sudden pyroclastic flow.

The institute recorded 335 earthquakes in the area of the volcano since Sunday and said more activity is expected in the next few days.

"These new strong, continuous earthquakes that we are now experiencing are due to fissuring, which means that there really is magma that is still making its way out of Taal," Bornas said.

"PHIVOCS strongly reiterates the need for the evacuation of Volcano Island, Taal Lake and the high-risk areas surrounding the volcano ... located within the immediate 14-kilometer radius from the main crater," she continued.

Eruption difficult to predict

Activity at the volcano continued through Tuesday. Lava fountains generated dark gray steam-laden plumes that reached 800 meters (2,624 feet) high, according to the institute. Volcanic lightening was also visible.

PHIVOLCS said that new vents had opened up on the volcano's northern flank and fresh ashfall had landed on nearby towns.

Photos from the eruption show ash mixing with rain, creating a thick black sludge that blanketed cars, streets, and homes in some towns. Ash is even heavier than snow, meaning excessive pile-ups, especially when mixed with rain, can cause roofs to collapse.

In a briefing with the media on Tuesday, PHIVOLCS director Renato Solidum said they cannot definitively tell when the eruptions will stop.

Photos: Taal volcano erupts in Philippines The landscape of Buso Buso is covered in ash on Sunday, January 19. Hide Caption 1 of 33 Photos: Taal volcano erupts in Philippines Clouds rise over the Taal volcano on January 19. Hide Caption 2 of 33 Photos: Taal volcano erupts in Philippines Evacuees rest at a government complex used as an evacuation center in Tagaytay on January 18. Hide Caption 3 of 33 Photos: Taal volcano erupts in Philippines A man clears ash from the roof of his truck at a fishing harbor in Laurel on January 17. Hide Caption 4 of 33 Photos: Taal volcano erupts in Philippines The Philippine province of Batangas is one of the areas affected by the eruption of the Taal volcano. Many animals had to be left behind as residents evacuated the danger zone. Hide Caption 5 of 33 Photos: Taal volcano erupts in Philippines Evacuees rest at an evacuation center in Batangas on Wednesday, January 15. Hide Caption 6 of 33 Photos: Taal volcano erupts in Philippines Volcano-affected residents ride along an ash-covered road on January 15. They were returning to evacuation centers after inspecting their homes in Agoncillo. Hide Caption 7 of 33 Photos: Taal volcano erupts in Philippines A volunteer carries a dog he rescued from deserted homes in Talisay. Hide Caption 8 of 33 Photos: Taal volcano erupts in Philippines Vegetation is burnt near the site of the volcano. Hide Caption 9 of 33 Photos: Taal volcano erupts in Philippines A family crosses a road that was damaged by volcanic tremors in Lemery. Hide Caption 10 of 33 Photos: Taal volcano erupts in Philippines A resident cleans ash from his roof in Agoncillo on Tuesday, January 14. Hide Caption 11 of 33 Photos: Taal volcano erupts in Philippines Volunteers save animals that were left behind in Batangas. Hide Caption 12 of 33 Photos: Taal volcano erupts in Philippines People watch the erupting volcano from Tagaytay on January 14. Hide Caption 13 of 33 Photos: Taal volcano erupts in Philippines Leila de Castro carries a religious statue recovered from a family member's house as she walks along an ash-covered road in Boso-Boso on January 14. Hide Caption 14 of 33 Photos: Taal volcano erupts in Philippines Men carry piglets that were rescued in Talisay on January 14. Hide Caption 15 of 33 Photos: Taal volcano erupts in Philippines Ash coats the roofs of homes in Tagaytay on January 14. Hide Caption 16 of 33 Photos: Taal volcano erupts in Philippines A resident cleans the roof of his house in Tagaytay. Hide Caption 17 of 33 Photos: Taal volcano erupts in Philippines Evacuees line up to have their children checked by medical personnel at an evacuation center in Tanauan. Hide Caption 18 of 33 Photos: Taal volcano erupts in Philippines A family flees to safer ground as the volcano produces ash in Tagaytay on Monday, January 13. Hide Caption 19 of 33 Photos: Taal volcano erupts in Philippines Erman Batan reacts over her missing husband, Roberto, whom she had not seen since they evacuated their home in Tagaytay on January 13. Hide Caption 20 of 33 Photos: Taal volcano erupts in Philippines Residents prepare their boats to evacuate Talisay on January 13. Hide Caption 21 of 33 Photos: Taal volcano erupts in Philippines Villagers rest on stairs in Batangas. Hide Caption 22 of 33 Photos: Taal volcano erupts in Philippines A youth rides an outrigger canoe while the volcano spews ash on January 13. Hide Caption 23 of 33 Photos: Taal volcano erupts in Philippines A Tanauan resident uses a shovel to clear mud and ash. Hide Caption 24 of 33 Photos: Taal volcano erupts in Philippines Lightning strikes as a column of ash surrounds the crater of the Taal volcano on Sunday, January 12. Hide Caption 25 of 33 Photos: Taal volcano erupts in Philippines People in Tagaytay watch plumes of smoke and ash rise from the volcano on January 12. Hide Caption 26 of 33 Photos: Taal volcano erupts in Philippines Villagers take shelter inside a church in Talisay. Hide Caption 27 of 33 Photos: Taal volcano erupts in Philippines Residents evacuate Tagaytay on January 12. Hide Caption 28 of 33 Photos: Taal volcano erupts in Philippines A column of ash surrounds the crater of the Taal volcano. Hide Caption 29 of 33 Photos: Taal volcano erupts in Philippines An ash column looms over Tagaytay. Hide Caption 30 of 33 Photos: Taal volcano erupts in Philippines Talisay residents use plastic bags to shield themselves from ash mixed with rainwater. Hide Caption 31 of 33 Photos: Taal volcano erupts in Philippines A Talisay resident splashes water on a vehicle covered in ash. Hide Caption 32 of 33 Photos: Taal volcano erupts in Philippines People take photos of the eruption on January 12. Hide Caption 33 of 33

The alert level for the volcano remains at four, meaning an "explosive eruption" could happen in the coming hours or days. Its highest alert level is five, indicating an eruption is taking place.

But predicting what will happen, or when, is fraught with difficulty. When the Taal Volcano erupted in 1754 it lasted six months. The deadliest eruption took 1,335 lives in 1911, and it lasted a few days.

"There is no smoking gun or mathematic indicator of if a volcano erupts or when," said Michalski of Hong Kong University.

Signals that eruptions are imminent or that there is activity going on include the frequency, location and depth of earthquakes, the water temperature of the lake increasing, and gas released from cracks or fissures.

"All these things, these activity increases, tell you that -- man, I'm getting out of here. Something is happening. But none of this says exactly what will happen in exactly what time frame," Michalski continued.

Ghost towns filled with ash

Houses with roofs covered with ash, spewed by Taal volcano in Tagaytay city, south of Manila on January 14, 2020.

Federal authorities are helping the response and evacuation operation. The army sent 20 military vehicles and 120 personnel to help affected residents, and the secretary of national defense said helicopters were on standby to evacuate people.

Aid organizations like the Red Cross are assisting on the ground by sending rescue vehicles and supplies.

Richard Gordon, Chairman of the Philippine Red Cross said evacuated areas look like "ghost towns" with houses "filled with ash."

"There's been some rain, many have collapsed already," Gordon said. "If you live in the area you'd probably be terrified."

In Batangas and Cavite towns, power is down due to heavy ash collecting on the electricity lines and there is no fresh water, Gordon said.

Evacuation centers include basketball courts, gyms and schools and are not designed for large-scale evacuations.

Red Cross teams on the ground are working to provide water tankers, ambulances, hot meal vans, and masks, as well as providing psychological support and setting up 70-bed wards in heavily affected areas to care for people with respiratory problems caused by the ash.

"The situation there is very dusty, and certainly it gets into your lungs and can create long-term damage," said Gordon. "We are advising people to close their windows with a damp cloth. People with respiratory illness or cardiovascular problems, they should move far away from the volcano to Manila or other provinces."

Evacuees from towns affected by the eruption of Taal volcano queue up to have their children checked by medical personnel at an evacuation center in Tanauan town, Batangas province.

The ash fall has also damaged crops in the area such as corn and coffee, and continues to threaten fish stocks, said Agriculture Secretary William Dar. Batangas province supplies Metro Manila with 40% of its harvest of fish, including tawilis or "live sardines" only found in the province.

A potential eruption could also bring long-term consequences for the area's economy.

The volcano is surrounded by a lake, which is a popular attraction -- meaning many of the towns in the vicinity are tourism hot spots. There are several amusement parks, lakeside resorts and yacht clubs within the 17-kilometer zone.

The holiday town of Tagaytay, which lies close to the water's edge, is a popular getaway for Manila residents who often take boats onto the lake and hike up the volcano.

On Sunday, the volcanic ash spread as far as Quezon City north of Manila, prompting the suspension of all flights at the capital's international airport. By Tuesday, normal operations resumed, according to the airport's general manager Ed Monreal, though it's possible flights may be suspended again if Taal's activity increases.

The airport remains congested with people trying to get on flights, Monreal added.