SAN JUAN, Puerto Rico (Reuters) - A dam in Puerto Rico weakened by heavy rains from Hurricane Maria was in danger of failing on Sunday, posing a flood threat to thousands of homes downstream as the storm-battered U.S. island territory struggled through a fifth day with virtually no electricity.

Some 70,000 people who inhabit a river valley below the Guajataca Dam in the northwestern corner of the island have been under evacuation orders since Friday afternoon, when authorities first warned that the earthen structure was in danger of imminent collapse.

The fear of a potentially catastrophic dam break added to the pandemonium facing disaster relief authorities in the aftermath of Maria, which has claimed at least 29 lives across the Caribbean, according to officials and media reports.

Puerto Rico Governor Ricardo Rossello personally urged residents of the area to heed evacuation orders after surveying damage to the dam on Saturday, telling reporters that a fissure in the structure “has become a significant rupture.”

The dam, which stands about 120 feet (37 meters) tall, was built in 1929 and supplies the surrounding region with hydropower, drinking water and irrigation supplies.

The National Weather Service in San Juan, the island’s capital, extended a flash flood watch for communities along the rain-swollen Guajataca River below the dam through midday Sunday.

If the dam were to fail, flooding would be life-threatening, the Weather Service warned. “Stay away or be swept away,” it said.

Maria, the second major hurricane to savage the Caribbean this month and the most powerful to strike Puerto Rico in nearly a century, carved a path of destruction through the island after plowing ashore early on Wednesday.

Arriving as a Category 4 storm on the Saffir-Simpson wind scale, with top winds of up to 155 mph (249.5 kph), Maria ripped roofs from buildings, turned roads into gushing debris-strewn rivers and knocked out power across the entire island, home to 3.4 million people.

‘WE LOST EVERYTHING’

“We lost our house, it was completely flooded,” said resident Carmen Gloria Lamb, a resident near the rain-swollen Guajataca. “We lost everything; cars, clothes, everything.”

Puerto Rico officials have officially confirmed 10 storm-related fatalities on the island, and the hurricane was blamed for at least 19 other deaths across the Caribbean, the bulk of them on the devastated island nation of Dominica.

Severe flooding, structural damage to homes and the loss of all electricity, except from backup generators, were three of the most pressing problems facing Puerto Ricans, New York Governor Andrew Cuomo, whose state is home to many of Puerto Rican descent, said during a tour of the island.

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“It’s a terrible immediate situation that requires assistance from the federal government, not just financial assistance,” he said on CNN on Saturday.

Even the island’s medical facilities have been left in precarious shape, with many hospitals flooded, strewn with rubble and running critically low on diesel fuel needed to keep generators operating. Evacuation to the U.S. mainland is the only option for some patients.

Signs of the strain on Puerto Ricans were evident throughout San Juan, the capital.

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Drivers had to wait up to seven hours at the few filling stations open on Saturday, according to news reports. Water rationing also began on Saturday. Signs posted throughout San Juan’s Old Town informed residents that service would return for two hours until further notice.

Telephone service also was unreliable, with many of the island’s cell towers damaged or destroyed.

On Sunday morning, the governor told reporters that officials would continue to clear roads and bridges blocked by the storm and that he would be joining a supply delivery mission to Caguas, a small city in the mountains south of San Juan.

The storm caused an estimated $45 billion of damage and lost economic activity across the Caribbean, with at least $30 billion of that in Puerto Rico, said Chuck Watson, a disaster modeler at Enki Research in Savannah, Georgia.

Maria, which was hundreds of miles (km) east of Florida over the Atlantic Ocean on Sunday, has been downgraded to a Category 2 storm and was expected to weaken further as it moves north in the Atlantic off the East Coast over the next two days.

Maria hit Puerto Rico about two weeks after Hurricane Irma, one of the most powerful Atlantic storms on record, killed more than 80 people in the Caribbean and the United States. The two storms followed Hurricane Harvey, which also killed more than 80 people when it struck Texas in late August and caused flooding in Houston.