A failing dam in Puerto Rico endangered tens of thousands of people and left officials scrambling to conduct mass evacuations on Friday.

"This is an EXTREMELY DANGEROUS SITUATION. Buses are currently evacuating people from the area as quickly as they can," the National Weather Service (NWS) in San Juan said in a statement.

Authorities were reportedly trying to save some 70,000 people.

There have been 13 deaths on the island since Hurricane Maria ripped through the Caribbean, leaving the entire US territory without power for the foreseeable future. The governor said that Maria was the worst storm Puerto Rico had seen in a century.

The dam, which is located at the northern end of Lake Guajataca in northwest Puerto Rico, forced NWS to send a series of tweets urging residents to get out of the path of the water.

The agency urged people to move to higher ground. Federal reservoir data shows that the lake rose more than three feet between Tuesday and Wednesday when the category 4 storm smashed into the island.

"This is an extremely dangerous and life-threatening situation. Do not attempt to travel unless you are fleeing an area subject to flooding or under an evacuation order," the agency said in that alert.

The dam is used for drinking water and irrigation in Puerto Rico. It was built in 1929, and had a capacity of 11 billion gallons in 1999, according to the US Geological Survey.

Maria came in quick succession after Hurricane Irma made its way through the Caribbean and up into Florida just weeks ago. Irma also hit Puerto Rico with strong wind, heavy rains, and knocked out power and communications for most of the island.

Animals take shelter from Hurricane Irma at Zoo Miami Show all 8 1 /8 Animals take shelter from Hurricane Irma at Zoo Miami Animals take shelter from Hurricane Irma at Zoo Miami Jennifer Nelson, senior keeper at Zoo Miami, leads a cheetah named Koda to a hurricane resistant structure within the zoo, Saturday, Sept. 9, 2017 in Miami. AP Photo/Wilfredo Lee Animals take shelter from Hurricane Irma at Zoo Miami Ryan Martinez, a trainer at Zoo Miami, places an Eurasion Eagle Owl into a crate AP Photo/Wilfredo Lee Animals take shelter from Hurricane Irma at Zoo Miami Flamingos at Zoo Miami, are shown in a temporary enclosure in a hurricane resistant structure within the zoo, (AP Photo/Wilfredo Lee) Animals take shelter from Hurricane Irma at Zoo Miami Brown pelicans and an American white pelican take refuge in a shelter ahead of the downfall of Hurricane Irma at the zoo in Miami REUTERS/Adrees Latif Animals take shelter from Hurricane Irma at Zoo Miami An African crested porcupine is moved into a shelter ahead of the downfall of Hurricane Irma at the zoo in Miami, Florida, REUTERS/Adrees Latif Animals take shelter from Hurricane Irma at Zoo Miami A macaw parrot looks out of it's cage after being put into a shelter REUTERS/Adrees Latif Animals take shelter from Hurricane Irma at Zoo Miami An African grey parrot is moved into a shelter ahead of the downfall of Hurricane Irma REUTERS/Adrees Latif Animals take shelter from Hurricane Irma at Zoo Miami Cheetahs are photographed in a shelter ahead of the downfall of Hurricane Irma at the zoo in Miami, Florida, REUTERS/Adrees Latif

The storm is now a category 3 hurricane, and is moving away from the Turks and Caicos Islands. It is expected to head northeast and east of the Bahamas over the weekend, according to forecasts.

So far, 30 people have been reported dead from the storm in the Caribbean from Maria. That includes at least 15 deaths in Dominica, where a further 20 people are missing.