Hurricane Fiona smashed through Puerto Rico on Monday with pounding rain and winds that triggered mudslides, “catastrophic” flooding and a power outage that swept across the entire island. Hundreds of thousands lacked running water.

More than 1,000 water rescues were performed and more were underway, Gov. Pedro Pierluisi said. Even as the storm made landfall Monday in the Dominican Republic, it continued to slam Puerto Rico with unrelenting rains — more than 30 inches in southern parts of the island.

The National Weather Service in San Juan urged residents to move to higher ground “immediately.”

“Heavy rainfall and catastrophic flooding continues across much of Puerto Rico,” said Richard Pasch, a specialist with the National Hurricane Center.

Authorities reported two deaths in Puerto Rico – one a 58-year-old man swept away by a flooded river in the inland town of Comerio and another one a 70-year-old man burned while trying to operate a generator. Another death was reported in the Dominican Republic, where a person was hit by a falling tree.

The Aqueduct and Sewer Authority said more than 800,000 customers – two-thirds of the homes and businesses – were without drinking water service. The entire power grid across the U.S. territory went down Sunday afternoon before the storm made landfall, leaving everyone without electricity.

Less than 10% had regained power Monday, and power distribution company LUMA Energy warned that it could take several days to fully restore electricity because of the outage’s magnitude.

“We have the equipment, tools and resources to respond to this event,” the company said.

The Dominican Republic government reported one death from falling trees because of the storm, which prompted at least four international airports to shut down, but by late afternoon Fiona was moving away from land. It could strengthen into a major hurricane by Tuesday.

In Puerto Rico, National Guard and Municipal Emergency Management personnel were helping with evacuations and water rescues in several communities of severely damaged Salinas in the south, Mayor Karilyn Bonilla Colón said. She urged residents to stay in their homes or shelters. The southern city of Ponce, the largest population center outside the San Juan metropolitan area, also experienced major flooding.