Power outages have cut off electricity across Puerto Rico, whose residents have already endured long periods of darkness after Hurricane Maria.

The island’s power authority said it could take between 24 and 36 hours to restore electricity throughout a US territory still struggling to recover from the storm’s lasting devastation.

“The entire electrical system in Puerto Rico collapses AGAIN! Back to September 20th”, the date Maria hit, San Juan Mayor Carmen Yulín Cruz said on Twitter.

An excavator caused the blackouts by accidentally felling a transmission line, authorities told the Associated Press.

Officials said they would focus on restoring power to hospitals, airports, banking centres and water systems.

A few hours into the blackout, power was back on at a half-dozen hospitals and medical centres. The main airport in San Juan remained open thanks to backup generators.

The outages were not expected to affect a Major League Baseball game scheduled to be played in San Juan, the capital, between the Minnesota Twins and the Cleveland Indians, whose star Puerto Rican shortstop Francisco Lindor brought a moment of joy to fans last night.

“The game will GO ON. Nothing will stop us”, Ms Cruz said.

Millions of residents were plunged into darkness after Maria pummelled Puerto Rico in September, inflicting severe damage on its electric grid. 

As the latest power outage demonstrated, efforts to restore the island’s infrastructure have been halting in the seven months since Maria made landfall. Last week, a tree toppled into a power line and wiped out service for some 870,000 customers.

Critics have accused the Trump administration of doing too little to aid the struggling territory. Senate minority leader Chuck Schumer, a New York Democrat, called the latest outage “unacceptable”.

“We can and must do more to help Puerto Rico recover and rebuild stronger. My office is in touch with the administration & hoping to get to the bottom of this ASAP”, he said on Twitter.