Puerto Rico’s governor, Wanda Vázquez, declared a state of emergency and activated the national guard on Tuesday after a series of earthquakes including one of magnitude 6.4 that was the most powerful to strike the Caribbean island in 102 years.

The quakes killed at least one person, provoked a protective power outage across the entire island and cut off drinking water to 300,000 customers, Vázquez told a news conference.

A priest inspects damage to the Parroquia Inmaculada Concepción church after a 6.4 earthquake hit just south of the island on Tuesday. Photograph: Eric Rojas/Getty Images

At least 346 people were left homeless, officials said, as homes were flattened, mostly in the south of the island. Many damaged buildings sat next to piles of rubble.

The declaration of emergency will facilitate federal financial aid for the US territory. Vázquez said she had been in contact with the Federal Emergency Management Agency (Fema).

Several members of Congress, including Florida’s two US senators and Puerto Rico’s non-voting member of the House of Representatives, appealed to Donald Trump for aid.

Trump has been briefed on the earthquakes and administration officials were monitoring the impact in coordination with Puerto Rico officials, the White House deputy press secretary, Judd Deere, said in a statement.

The island has been rocked by a series of quakes – literally hundreds – since 28 December, including 10 of magnitude 4 or greater, the US Geological Survey said.

Store owners remove supplies from Ely Mer Mar hardware store, which partially collapsed after an earthquake struck Guanica, Puerto Rico, on Tuesday. Photograph: Carlos Giusti/AP

A 5.8-magnitude temblor on Monday damaged some homes on the southern coast.

Powerful quakes are rare in Puerto Rico, and Tuesday’s 6.4 was the strongest in more than a century, the island’s seismology office, Red Sísmica, said.

On 11 October 1918, a 7.3 magnitude quake and tsunami killed 116 people in Puerto Rico, according to Red Sísmica data.

The US territory is still recovering from the devastation of Hurricane Maria in 2017, which killed about 3,000 people and destroyed a significant amount of infrastructure. The island suffered during Hurricane Irma around the same time, as the climate crisis continues to exacerbate such storms.

Puerto Rico is also working through a bankruptcy process to restructure about $120bn of debt and pension obligations.

“We are a resilient people. We have responded to many difficult situations. Now this has been asked of us one more time,” said Vázquez, who later toured damaged areas.

One of Tuesday’s quakes triggered an automatic shutdown of electricity across the island as a safety measure and a later, more powerful quake damaged power plants in the southern part of the island, Vázquez said.

Power remained cut off to the capital San Juan and most of the island some 11 hours after the largest quake.

Puerto Rico was producing only 40 megawatts of electricity when demand was close to 2,000 megawatts, Ángel Figueroa, president of the electricity workers’ union Utier, said on Twitter.

Some 300,000 of Puerto Rico’s 1.3 million water customers lacked service, Vázquez said. The governor confirmed one death, as reported by El Nuevo Día, that a 73-year-old man died after a wall fell on him.

A man walks past a destroyed store after a 6.4 earthquake hit on Tuesday in Guánica, Puerto Rico. Photograph: Eric Rojas/Getty Images

But she said it was too soon to offer an accurate assessment of damage or injuries.

Vázquez, who assumed office in August after Ricardo Rosselló stepped down in the face of massive street protests, repeated pleas for people to remain calm and asked people to check on neighbors, especially the elderly.

The biggest quake on Tuesday, of magnitude 6.4, struck at a depth of six miles at 4.24am, near Ponce in the south, the US Geological Survey said.

Witnesses using social media described it as “super strong” and lasting up to 30 seconds, followed by a number of hefty aftershocks.

The international airport near San Juan continued normal service with the help of power generators, El Nuevo Día reported, citing Jorge Hernández, chief executive of Aerostar Airport Holdings.

On Tuesday evening, US House speaker Nancy Pelosi was reported as urging the Trump administration to respond to Puerto Rico’s plea for emergency status and accompanying aid.