70,000 people have been evacuated after a dam failure on a river in Puerto Rico caused "extremely dangerous" flooding.

Residents of the towns of Isabela and Quebradillas were evacuated from their homes on buses after a crack in the Guajataca Dam caused a "life-threatening situation" the National Weather Service (NWS) reported.

The 345-yard (316-metre) dam, which was constructed decades ago, holds back a man-made lake covering about two sq miles (five sq km). The dam failed at 14:10 local time (18:10 GMT) resulting in flash flooding.

Warning residents to leave or move to higher ground the NWS tweeted:

"This is an EXTREMELY DANGEROUS SITUATION. Buses are currently evacuating people from the area as quickly as they can,"

"All Areas surrounding the Guajataca River should evacuate NOW. Their lives are in DANGER! Please SHARE!"

Responding to the emergency Governor Ricardo Rossello said from the capital, San Juan: "It's a structural failure. I don't have any more details. We're trying to evacuate as many people as possible."

The dam failure occurred in the aftermath of Hurricane Maria which tore through Puerto Rico, leaving 13 people dead.

With winds of 140mph, the category three storm left a trail of devastation in its wake and 3.4 million of the US island territory's residents are without electricity.

The governor of Puerto Rico has called Maria the worst hurricane in a century while US President Donald Trump said the region had been "totally obliterated" by the storm.

Maria also caused widespread destruction on the small island of Dominica when it hit on Monday night, leaving at least 15 dead and 20 missing. The storm is now moving away from the Turks and Caicos Islands.

It is expected to head to the northeast and east of the Bahamas over the weekend, forecasters say The Guardian reports.