Manila, Philippines (CNN) Flooding unleashed by a deadly, slow-moving typhoon has invaded more towns in the northern Philippines, forcing people to clamber onto rooftops to await rescue.

Typhoon Koppu began battering the region over the weekend, driving tens of thousands from their homes.

At least 18 people -- all but one in Luzon, the Philippines' largest and most populous island -- died as a result, Philippines' disaster management agency director Alexander Pama said. Another 16 were injured, while one person was missing Tuesday.

The storm, known as Lando in the Philippines, has directly affected more than 550,000 people, with more than 107,000 taking refuge in shelters as of Tuesday.

The storm came ashore early Sunday at super typhoon strength, ripping roofs off buildings and uprooting trees in the coastal province of Aurora.

The fierce storm lumbered around Luzon at an excruciatingly slow pace, setting off floods and landslides across the rugged terrain.

Floodwaters have engulfed San Antonio in central Luzon, Mayor Antonino Lustre said Monday, according to CNN affiliate ABS-CBN. Rescuers were unable to reach some areas, where residents were stranded on roofs, the broadcaster reported.

Floodwaters have wreaked havoc in other towns in Nueva Ecija province, Gov. Aurelio Umali said, according to ABS-CBN.

JUST WATCHED Super Typhoon Koppu makes landfall Replay More Videos ... MUST WATCH Super Typhoon Koppu makes landfall 01:14

Initial estimates suggest the storm has caused at least 5.3 billion pesos, or $114 million, in damage to infrastructure and agriculture, though Pama noted that number will likely rise.

"We know a lot of infrastructure has been destroyed, (and) some hasn't been estimated yet," he said. "Also, the (damage cost for) private properties like houses are still not included."

Towns reportedly cut off by landslides, floods

The storm packed maximum sustained winds of 240 kilometers per hour (150 mph) when it slammed into the eastern coast of Luzon, according to the U.S. military's Joint Typhoon Warning Center, although the Philippines' national weather agency measured the winds as significantly weaker, at 185 kilometers per hour.

Flooding and landslides have cut off roads and communications in three towns in Aurora province, including Casiguran, where the typhoon made landfall, authorities reported.

"Based on the report of the Philippine army, there were many houses destroyed and trees uprooted in the three towns," the official Philippines News Agency said. The army and other agencies worked to clear the routes to Casiguran, which has about 25,000 people, and to Dinalungan and Dilasag, it reported.

By Tuesday, all roads to and from Casiguran were again passable, according to Nigel Lontoc, a civil defense official in central Luzon. Authorities had packed food for about 1,000 families in the hard-hit community.

Roads have also been cleared in Baler, another town in Aurora, where CNN Philippines reporter Paul Garcia reported flooding in several neighborhoods. Surprised local residents said that while storms are common in the area, flooding is not, Garcia reported.

Heavy rains currently lashing Baler. Four barangays now flooded #LandoPh | @cnnphilippines pic.twitter.com/095RpRSnDE — Paul Adrian Garcia (@MrPaulGarcia) October 18, 2015

The heavily populated region around Manila, the Philippine capital, wasn't in Koppu's direct path, but still got lashed with wind and rain.

One of those killed -- a 14-year-old boy struck by a falling tree -- was in Quezon City. Another was a 62-year-old woman hit by a wall that collapsed in Subic, northwest of the capital.

Huge rainfall expected

A big concern is the extreme amounts of rain Koppu is expected to unleash. Flooding has struck Cabiao, Jaen and Santa Rosa.

"The big story out of this storm is definitely going to be the rainfall totals," said CNN meteorologist Allison Chinchar. Some areas were forecast to receive more than 1 meter (39 inches) of rain by the end of Wednesday.

San Pedro bridge in Maddela yesterday vs today #typhoon Koppu #LandoPH pic.twitter.com/Da55oo8G7m — James Reynolds (@EarthUncutTV) October 18, 2015

The typhoon was predicted to dawdle across northern Luzon for days because of a ridge of high pressure over China blocking its progress farther north.

"That's where the problem with the flash flooding comes in, because when you have all of this rain that keeps coming down over the same places over and over, that is likely to trigger mudslides and landslides in addition to flash flooding problems in ... some of the low-lying areas," Chinchar said.

Officials reported dozens of flight cancellations, thousands of people stranded in ports and many municipalities without power.

'The bowling alley for typhoons'

Situated in the Western Pacific, the Philippines is frequently hit by typhoons.

"They're located in the belt basically between the equator and the subtropics. You might consider it the bowling alley for typhoons moving across the Pacific," said Bob Henson, a weather and climate science blogger for Weather Underground.

"It's considered to be the most vulnerable large nation on Earth for tropical cyclones," he said.

The deadliest storm to hit the country in recent years was super Typhoon Haiyan , which left more than 7,000 people dead or missing in November 2013.

Haiyan, one of the strongest storms ever to make landfall, generated a devastating storm surge that flattened entire neighborhoods in the densely populated coastal city of Tacloban before moving quickly over other areas of the central Philippines.