The 1920's era earthen dam on the Guajataca River in northwest Puerto Rico cracked on Friday, prompting the government to issue an order for 70,000 people in downstream towns to evacuate.
Most people living near a crumbling dam in storm-battered Puerto Rico have been moved to safety, Governor Ricardo Rossello said on Monday, as he urged the US Congress to fund an aid package to avert a humanitarian crisis after Hurricane Maria.
The drama unfolded as the US island territory, working without electricity, struggled to dig out and clean up from its disastrous brush with the hurricane, blamed for at least 33 deaths across the Caribbean.
There have been growing concerns for some 70,000 people who live in the river valley below the Guajataca Dam in the island's northwest, where cracks were seen appearing on Friday in the 88-year-old earthen structure.
Late Saturday, however, the governor's office said it was impossible to determine exactly how many people were ordered out by local mayors because they do not have working phones and the government has been unable to contact them.
On Friday, public safety chief Hector Pesquera had cited a different cause for the initial dam failure, according to the newspaper El Vocero. Pesquera said a drain which normally releases water from the dam in a controlled fashion had broken, sending it gushing out in torrents.
Puerto Rico was already battling dangerous floods elsewhere on the island because of Hurricane Maria, which hit before dawn Wednesday as part of its furious tear across the Caribbean.
Governor Ricardo Rossello visited Isabela, an area near the dam, late Friday and urged people to get out. The government is also sending in buses to take people to higher ground.
As the island is without power but for emergency generators, and without telecommunications, the governor's entourage left a satellite phone with the mayor of Isabela so he can talk to crews manning the dam.
Rossello has called Maria the most devastating storm to hit the island in a century.
In its latest update at 2100 GMT, the US National Hurricane Center said Maria was moving northwest and located 285 miles (460 km) east of Great Abaco Island in the Bahamas.
So far, at least 33 people have been confirmed dead as a result of Hurricane Maria, including 15 in Dominica, three in Haiti and two in Guadeloupe.
Of the 13 victims in Puerto Rico, eight died in the northern town of Toa Baja, one of the worst-hit areas which was ravaged by winds of more than 125 miles per hour (200 kilometres per hour) and then hit by flooding when the island's largest river, La Plata, burst its banks.
It was also a distressing day for Marina Montalbo, 36, a secretary from Isabela. She was trying to rest in a shelter with her husband and her 11-month-old baby.
"They made us evacuate. It was a really difficult thing to have to do," she said, sobbing. "We just had to get out; they were screaming that we had to get out."
Aid ships trying to dock
Across the island, streets were littered with debris from the storm, with toppled trees, street signs and power cables strewn everywhere.
The torrential rain also turned some roads into muddy brown rivers, impassable to all but the largest of vehicles.
Puerto Rico's electricity network has been crippled by the storm and engineers say it could take months for power to be fully restored.
US federal emergency chief Brock Long said ships carrying millions of meals and bottles of water were trying to dock as the island's ports are slowly reopened.
Before reaching Puerto Rico, the storm devastated the small island nation of Dominica.
And after striking Puerto Rico, the storm headed west toward the Dominican Republic where it damaged nearly 5,000 homes, forcing the evacuation of more than 18,000 people, the president's office said.