Hurricane Fiona bore down on the Dominican Republic Monday after knocking out the power grid and unleashing floods and landslides in Puerto Rico, where the governor said the damage was "catastrophic."
No deaths have been reported, but authorities in the US territory said it was too early to estimate the damage from a storm that was still forecast to unleash torrential rain.
Up to 30 inches (76 centimeters) was forecast for Puerto Rico's southern region.
"It's important people understand that this is not over," said Ernesto Morales, a meteorologist with the National Weather Service in San Juan.
He said flooding reached "historic levels," with authorities evacuating or rescuing hundreds of people across the island.
"The damages that we are seeing are catastrophic," said Governor Pedro Pierluisi.
The storm washed away a bridge in the central mountain town of Utuado that police say was installed by the National Guard after Hurricane Maria hit in 2017.
Large landslides were reported, with water rushing down big slabs of broken asphalt and into gullies.
Winds of up to 85mph have also been reported and millions of people have been left without power.
Fiona landed just two days before the anniversary of Hurricane Maria, which hit on September 20, 2017, causing nearly 3,000 deaths.
Luma, the company that operates power transmission and distribution, said bad weather had disrupted transmission lines, leading to “a blackout on all the island.”
“Current weather conditions are extremely dangerous and are hindering our capacity to evaluate the complete situation,” it said, adding that it could take several days to fully restore power.
The storm was forecast to pummel cities and towns along Puerto Rico’s southern coast that have not yet fully recovered from a string of strong earthquakes starting in late 2019.
More than 1,000 people with some 80 pets had sought shelter across the island by Sunday night, the majority of them in the southern coast.