Maria weakened into a category 4 hurricane as it hit land, making it the first of its kind to hit Puerto Rico since 1932.
One of the strongest hurricanes to ever hit Puerto Rico pummeled the island on Wednesday as officials warned it would decimate the power company's crumbling infrastructure and force the government to rebuild dozens of communities.
Maria made landfall early Wednesday in the southeast coastal town of Yabucoa as a Category 4 storm with winds of 250 kph (155 mph) winds, and it was expected to punish the island with life-threatening winds for 12 to 24 hours, forecasters said.
Maria had previously been a Category 5 storm with 281 kph (175 mph) winds.
"This is going to be an extremely violent phenomenon," Gov. Ricardo Rossello said. "We have not experienced an event of this magnitude in our modern history."
Metal roofs were already flying and windows were breaking as the storm approached before dawn, with nearly 900,000 people without power and one tree falling on an ambulance.
Those who sought shelter at a coliseum in San Juan were moved to the building's second and third floors, reported radio station WKAQ 580 AM. The storm was moving across Puerto Rico on Wednesday morning at 17 kph (10 mph), with a gust of 182 kph (113 mph) reported in the capital of San Juan, according to the US National Hurricane Center in Miami.
Maria ties for the eighth strongest storm in Atlantic history, when measured by wind speed. Coming in second is this year's Irma, which had 300 kph (185 mph) winds and killed 38 people in the Caribbean and another 36 in the U.S. earlier this month.
Puerto Rico had long been spared from a direct hit by hurricanes that tend to veer north or south of the island. The last Category 4 hurricane landfall in Puerto Rico occurred in 1932, and the strongest storm to ever hit the island was San Felipe in 1928 with winds of 258 kph (160 mph).
As Maria approached, US President Donald Trump offered his support via Twitter.
Puerto Rico being hit hard by new monster Hurricane. Be careful, our hearts are with you- will be there to help!— Donald J. Trump (@realDonaldTrump) September 20, 2017
More than 4,400 people were in shelters by late Tuesday, along with 105 pets, Rossello said.
The storm's center passed near or over St Croix overnight Tuesday, prompting US Virgin Islands Governor Kenneth Mapp to insist that people remain alert. St Croix was largely spared the widespread damage caused by Hurricane Irma on the chain's St Thomas and St John islands just two weeks ago. But this time, the island would experience five hours of hurricane force winds, Mapp said.
Maria killed one person in the French Caribbean island of Guadeloupe when a tree fell on them Tuesday, and two people aboard a boat were reported missing off La Desirade island, just east of Guadeloupe, officials said.