A dam in northwest Puerto Rico is failing, causing flash flooding and prompting emergency evacuations Friday, the National Weather Service said.

Operators of the Guajataca Dam said it failed at 2:10 p.m. ET, prompting the NWS to issue a flash flood emergency warning for Isabela and Quebradillas municipalities, home to some 70,000 people, the agency said in tweets that went unseen by many in the blacked-out coastal area.

"This is an EXTREMELY DANGEROUS SITUATION. Busses are currently evacuating people from the area as quickly as they can," NWS San Juan said.

A flash flood warning has been put in place for eastern Isabela and western Quebradillas until 2 a.m. NWS San Juan is telling residents along the Guajataca River to "seek higher ground now!"

Details remained sketchy about the evacuation with communications hampered after the storm. The 345-yard (316-meter) dam holds back a manmade lake covering about 2 square miles and was built decades ago, U.S. government records show.

"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," an alert on the NWS website said.



The island is still reeling from a direct hit by Hurricane Maria, knocking out power and communications to most of the island.

Officials said 1,360 of the island's 1,600 cell-phone towers had been downed, and 85 percent of above-ground and underground phone and internet cables were knocked out. With roads blocked and phones dead, officials said, the situation may be worse than they know.

Federal reservoir data show that the lake behind the dam, Lago de Guajataca, rose more than three feet between Tuesday and Wednesday, when the hurricane hit as a Category 4 storm. More recent data were unavailable.



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

Danica Coto of The Associated Press contributed to this report.