SAN JUAN - Some 70,000 people have been ordered to evacuate their homes after a rain-swollen dam in Puerto Rico failed in the latest disaster caused by Hurricane Maria, which was on Saturday expected to head into open waters.

With the storm death toll standing at 33 across the Caribbean, Puerto Rico's National Weather Service issued a flash flood warning for people living along the Guajataca River in the northwest of the island, saying an earthen dam there was in danger of collapsing. "All Areas surrounding the Guajataca River should evacuate NOW. Their lives are in DANGER!," the NWS tweeted on Friday, saying flooding had already begun downstream.

Governor Ricardo Rossello also issued an order for 70,000 people living in the area to flee. Public safety chief Hector Pesquera said a drain which normally releases water from the dam in a controlled fashion had stopped working, the El Vocero daily reported.

Footage from WeatherNation TV showed water gushing down a ramp-style conduit, washing away huge chunks of soil from the grassy green slopes of the dam.

Early on Saturday, the NWS extended the warning to the western Quebradillas and eastern Isabela areas, home to another 8,000 people.

Puerto Rico was already battling dangerous floods after Hurricane Maria hit early Wednesday, devastating the Caribbean island.

Rossello has called Maria the most devastating storm in a century after it destroyed the US territory's electricity and telecommunications infrastructure.

So far, a preliminary assessment said 13 people had died as a result of the storm, he told CNN.

"Right now our efforts are to make sure we have everybody safe, that we can rescue people. Our efforts have already produced almost 700 rescues so we're clearly focused on that."

In its latest update at 0900 GMT, the US National Hurricane Center said Maria was tilting toward the western Atlantic and away from the Bahamas, where storm warnings were discontinued.

It was a welcome reprieve for the archipelago that had already been badly battered by Hurricane Irma earlier this month.

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.

After speaking with Puerto Rico's governor on Thursday night, US President Donald Trump promised to speed up relief efforts.

Of the 13 victims, 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 kilometers per hour) and then hit by flooding when the island's largest river, La Plata, burst its banks.

Many residents did not evacuate on time, while others say they never heard the warning sirens.

Others could be seen returning home after several days away to begin the arduous process of clearing their homes of the heavy mud left by the floodwaters in order to start the process of rebuilding.

Marisol Rosario, a 55-year-old housewife who fled with her husband, said the violent winds forced her to flee without taking their dog.

"I thought I would find him dead, but he managed to climb on top of the furniture and survive," she said tearfully.

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.

The local electricity board has pledged to prioritize restoring power to hospitals, water treatment plants and pumping stations.

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.

After devastating 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.

By Saturday morning, Maria had been downgraded to a Category Three hurricane with winds of 120 miles per hour which was churning in the sea some 340 miles east of the central Bahamas.