Puerto Rican officials rushed to evacuate some 70,000 people downstream of a failing dam in the wake of Hurricane Maria, while at least six people were confirmed dead on the US Caribbean territory following the storm.

The US National Weather Service (NWS) issued a flash flood emergency at the Guajataca Dam in Isabela Municipality, saying on Twitter that it was "an extremely dangerous situation" and that buses were evacuating residents from their homes "as quickly as they can".

Dam operators had reported that the dam was "failing causing flash flooding downstream", the service said.

"All Areas surrounding the Guajataca River should evacuate NOW. Their lives are in DANGER!," the service said later.

An engineer inspecting the dam reported a "contained breach" that officials quickly realised was a crack that could be the first sign of the total failure of the dam, said Anthony Reynes, a meteorologist with NWS.

Flash Flood Warning for eastern Isabela & western Quebradillas until 2AM. Residents along Guajataca River seek higher ground now! #prwx pic.twitter.com/h6DcKN3KG3 — NWS San Juan (@NWSSanJuan) September 23, 2017

The evacuation came as at least six people were confirmed dead in Puerto Rico after Hurricane Maria pummelled the region.

Puerto Rican public safety officials confirmed six deaths, while the governor separately put the figure at 13.

Puerto Rico is grappling with the largest municipal debt crisis in US history, with both its government and the public utility having filed for bankruptcy protection amid disputes with creditors.

Al Jazeera's Andy Gallacher, reporting from San Juan, said the news about the damaged dam "really goes to the failure of Puerto Rico's infrastructure".

He added: "This island is $73bn in debt, and that means there's been no investment in things like reservoirs, lakes and dams, and of course, power, which is here the biggest problem."

Destructive storm

Hurricane Maria had left more than 30 dead as it churned across the Caribbean, according to media reports. The death toll was expected to rise as recovery efforts continued, with many areas still cut off from contact with authorities.

The Category 3 storm was about 185km east-north-east of the southeastern Bahamas on Friday evening, with winds of 205 kilometres per hour. Tropical storm warnings were in place for the Bahamas, the US National Hurricane Center said in its 5pm EDT (21:00 GMT) advisory.

Rainfall of up to 50 centimetres was expected on the Turks and Caicos islands. The storm was expected to have brought up to 100cm of rain to some areas of Puerto Rico, forecasters said.

READ MORE: Hurricane Maria kills dozens as it lashes Caribbean islands

Puerto Rico, where some of the population of 3.4 million had been without power since Hurricane Irma in early September, was completely blacked out after Maria. Authorities were warning of power outages lasting for months.

US President Donald Trump pledged support to both Puerto Rico and the US Virgin Islands as they recover from hurricanes Maria and Irma, the White House said.