Puerto Rico's governor declared a state of emergency on Tuesday after a series of earthquakes killed at least one person, toppled buildings and knocked out power to nearly the entire island of more than 3 million people.

The largest of the quakes in the US territory registered at magnitude 6.4, the most powerful to hit the Caribbean island in 102 years.

With two large power plants shut down, drinking water was cut off to at least 300,000 customers, Wanda Vazquez, the governor, told a news conference.

She said power should be restored to most of the island within 24 to 48 hours. Puerto Rico schools will remain closed and public employees, other than health workers and police, will stay home on Wednesday while checks are made on the structural safety of buildings, Ms Vazquez said.

"There are people who have lost their lives, there are people who have lost all their property," She told reporters, without giving further details on the extent of damage and injuries.