Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

A 6.4-magnitude earthquake struck Puerto Rico early Tuesday, killing at least one person and causing a power outage across the island, as well as structural damage to roads and bridges especially in the southwestern region.

There have been at least 51 aftershocks since the earthquake, the largest in a series of quakes, hit at 4:24 a.m. Federal agencies monitoring the seismic activity say the tremors and quakes could continue for the next few days, according to Gov. Wanda Vázquez.

At a press conference Tuesday morning, Vázquez announced the island is in an official state of emergency.

"We've never been exposed to this kind of emergency in 102 years," she said in Spanish.

A collapsed home after an earthquake in Guanica, Puerto Rico, on Jan. 7, 2020. Reuters TV

Government offices and schools were closed, and some hospitals, especially in the southwestern region, were evacuated for safety reasons. Residents, especially in the south, have been terrified to go into their homes for fear that another quake will bring the structures down.

"Every single one of you know how your homes were built. Don't put yourselves at risk. Your homes can be replaced but we can't replace your or your children's lives," Vázquez said.

She urged citizens to stay calm and asked public employees to stay home while authorities assess the damages. First responders, the governor said, were reporting to their usual areas.

"Citizen security is a priority, so vulnerable areas are being inspected and all necessary measures will be taken to ensure the safety of all Puerto Ricans,” Vásquez said.

Sen. Rick Scott, R-Fla., tweeted that he had been in contact with President Donald Trump and with the Federal Emergency Management Agency about the situation in Puerto Rico.

Vázquez said on Tuesday morning that she had not received any communications from Trump as of 11 a.m.

On Tuesday afternoon, the White House said in a statement that the president has been briefed on the situation and "will continue to monitor the effects and coordinate with Puerto Rico officials."

A FEMA spokesperson later told NBC News in a statement that it had received Vázquez's request for a federal emergency declaration, but that the request is still "under consideration." FEMA personnel already on the island are "working closely with Puerto Rico Emergency Management Bureau." The agency also "deployed two Incident Management Assistance Teams to the island" and activated certain regional response teams to help.

Late on Tuesday night, Vázquez tweeted that she received a call from FEMA notifying her that Trump "signed our Emergency Declaration request for Puerto Rico."

"People don't feel safe"

In the southern city of Ponce, a man died after an inner wall that was under construction in his house collapsed during the quake. The victim was identified as Nelson Martínez, 73. Ray González, a family member, told Telemundo he was woken up by "the big noise" of the wall collapsing.

The Morning Rundown Get a head start on the morning's top stories. This site is protected by recaptcha

Ponce, one of the island's largest cities, has no power, intermittent access to water and is grappling with landslides affecting its main highway.

Ponce Mayor María "Mayita" Meléndez told NBC News that at least nine other people in her city were injured.

Residents scared to go back into their homes are seeking refuge inside their cars parked in open areas and public parking lots, she said.

"People don't feel safe," she added. "We are living moments of uncertainty."

Meléndez said her municipality is putting up tents in open areas and parks for people looking for refuge, away from structures that could collapse. According to her, five hospitals in the area are functional.

Albert Rodríguez, who is from the southwest town of Guánica, said tsunami sirens went off before officials canceled the alert. He said there is widespread damage in his neighborhood.

“The road is cracked in the middle and it lifted up,” he said.

Part of the widespread destruction in Rodríguez's town includes a public school near the earthquake's epicenter.

The school, Agripina Seda, collapsed because of the widespread quakes. César González of the Puerto Rico Department of Education told Telemundo that the school is the one with the "the biggest damages" he's seen so far. Other schools in the area have reported less damage.

González added that the roughly 200 students who attend the school will most likely have to be relocated to other schools.

Eligio Hernández, Puerto Rico's Education Secretary, said that classes in public schools will be indefinitely postponed until the government inspects all school buildings this week.

Puerto Rican Housing Secretary Fernando Gil Enseñat said during the press conference that nearly 400 people are housed in shelters in at least five municipalities. Over 200 sought shelter in Guánica, 40 in Ponce and 56 in the town of San Germán.

The governor said that power is slowly being restored. The island's main hospital, Centro Médico, now has electricity.

José Ortiz, the head of the island's power authority, said at the governor's press conference, "It's not going to be like Maria," referring to the hurricane that resulted in power outages for more than a year. Ortiz said he expects the entire island to have power in the next few days.

About 300,000 customers who get their water supply through electrical water pumps in Puerto Rico don't have access to water in their homes.

Nelson Torres Yordán, the mayor of the southwest town of Guayanilla, said at a press conference that about 120 people are housed in shelters in the municipality. At least three people in his town have been injured, including a baby.

Torres Yordán said that the power authority told him that Guayanilla will have its power fully restored in the next two weeks.

Tuesday's earthquake follows the 5.8-magnitude one that struck early Monday, collapsing five homes in Guánica and heavily damaging dozens of others.

Puerto Rico's residents have been feeling tremors since Dec. 28, and the last two earthquakes have set islanders on edge as they grapple with the uncertainty of what comes next.

Victor Huerfano, director of Puerto Rico's Seismic Network, told The Associated Press that shallow quakes were occurring along three faults in Puerto Rico’s southwest region: Lajas Valley, Montalva Point and the Guayanilla Canyon.

He said the quakes overall come as the North American plate and the Caribbean plate squeeze Puerto Rico.

One of the island's most iconic landmarks, the Guánica Lighthouse, built by the Spanish in 1892, suffered damage after the earthquake. Although the lighthouse's tower survived, one of its front walls collapsed.

The quake also collapsed a coastal rock formation that had formed a sort of rounded window, Punta Ventana, a popular tourist draw in Guayanilla.