Guanica, Puerto Rico CNN  — 

Hours after a deadly 6.4 magnitude earthquake rocked Puerto Rico, people on the southern coast fear more homes could collapse and most of the people on the island remain without power.

Tuesday’s quake – the strongest and likely the most damaging of a series of quakes that have hit the island since December 28 – left a man dead, caused dozens of homes and structures to crumble and cut power and water service to swaths of the island.

Gov. Wanda Vázquez Garced declared a state of emergency and activated the Puerto Rico National Guard as she pleaded with people to remain calm and prepare for aftershocks.

“We have responded to many difficult situations, and here we are once again,” Vázquez said.

Engineers were working to reestablish service to close to 300,000 of the island’s 1.1 million utility customers who were without water service Tuesday, Vázquez said.

The 6.4 quake struck at 4:24 a.m. (3:24 a.m. ET). It centered off Puerto Rico’s southern coast, about 6 miles south Indios, a town of about 1,500 people, the US Geological Survey said. Several aftershocks followed, including a magnitude 5.6 temblor striking south of Indios at 7:18 a.m., USGS said.

In Guanica, families sat on white plastic chairs and cots in the parking lot of the Mariano “Tito” Rodriguez Municipal Coliseum. About 255 have taken shelter there since a 5.8 magnitude quake shook the US territory Monday, but officials now fear the building is not stable.

Dozens of families are taking shelter outside a local coliseum in Guanica.

“My home is like a hammock,” Guanica resident Hector Cruz said. “It’s like a drill coming from underneath the home.”

The earthquakes come after Hurricane Maria devastated the US territory in September 2017, and many in southern Puerto Rico say the earthquakes’ damage is worse.

“There’s no warnings for this,” Puerto Rico Police Commissioner Henry Escalera said of the earthquakes. “A hurricane gives us time to plan ahead.”