It tore roofs from buildings, snapped power lines and turned roadways into torrents laden with debris as it cut a diagonal swath across the island.
The entire island of 3.4 million people was under a flash flood warning yesterday as the storm was forecast to dump 50cm to 75cm of rain on much of Puerto Rico through until tomorrow, according to the US National Hurricane Centre.
The island's governor, Ricardo Rossello, said the only fatality immediately reported was a man struck by a piece of lumber hurled by high winds.
"It's nothing short of a major disaster," Rossello said in a CNN interview, adding it may take months for the island's electricity to be completely restored. Earlier he imposed a dusk-to-dawn curfew for the island.
The streets of Puerto Rico's historic Old Town in the capital, San Juan, were strewn with broken balconies, air conditioning units, shattered lamp posts, fallen power lines and dead birds. Few trees escaped unscathed.
The island's recovery could be complicated by its financial woes as it faces the largest municipal debt crisis in US history. Both its Government and the public utility have filed for bankruptcy protection amid disputes with creditors.
Maria weakened as it went over land in Puerto Rico and picked up strength as it passed over warm Caribbean waters.
It was a Category 3 storm with maximum sustained winds of 185km/h about 90km north of Punta Cana, on the east coast of the Dominican Republic, last night.
Punta Cana was hit with wind gusts of 93km/h and Maria was forecast to bring storm surges of up to 1.85m in the Dominican Republic.
Maria was expected to pick up strength as it churns toward the Turks and Caicos Islands and the southeastern Bahamas today. Storm surges on the islands could be as high as 3.5m.
Maria would then move north in the Atlantic Ocean over the weekend and there was no indication as to whether it would hit the continental United States.
It was classified a Category 5 storm when it struck the eastern Caribbean island nation of Dominica on Tuesday with devastating force.
Based on an aerial survey, about 95 per cent of roofs were damaged or destroyed by Maria in Dominica, one of the poorest countries in the Caribbean with a population of about 73,000.