(CNN) With most of Puerto Rico in the dark Wednesday night, Gov. Ricardo Rossello said in a tweet that he has suggested Puerto Rico's Electric Power Authority cancel its contract with a subcontractor that caused an island-wide power outage.

An excavator operated by D. Grimm, a subcontractor for Cobra Acquisitions, apparently caused the blackout, which originated at a major transmission line running between Salinas and Guayama in the southeast, according to the authority.

The same company was responsible for an outage that affected 870,000 customers after a tree fell on a power line last week, PREPA said.

Mammoth Energy, Cobra's parent company, said workers were removing a fallen tower when the machine got too close to an energized line and an electrical ground fault caused the outage.

As of 8 p.m., only 334,000 customers in the US commonwealth had electricity again. Power was to be restored to customers who had electricity before the latest outage within 24 to 36 hours, the authority said.

This is the latest setback as power officials try to restore power to the nearly 1.4 million customers who lost electric service during Hurricane Maria nearly seven months ago. Most of the island had had its power restored as the commonwealth rebuilt its decimated electrical grid.

Hospitals first

The utility said its priority Wednesday was to bring back service to medical facilities, water pumping systems and financial institutions.

Video and photos posted on social media showed rapid transit line workers helping down passengers from stalled trains and college students registering for classes during the blackout. Long lines of cars formed at gas stations and a fire broke out in an electrical generator behind a restaurant in the Condado tourist district.

"Seven months after Maria, we are back where Maria left us," Cynthia Garcia Coll, a professor at Carlos Albizu University in San Juan, said via email.

Rafael Santiago, an engineer at a plant that makes prosthetic devices, said via Twitter that he and other workers were evacuated after being locked inside for about 20 minutes while electric generators were started.

San Juan Mayor Carmen Yulin Cruz, a frequent critic of recovery efforts since the September hurricane, worried that Puerto Rico won't be prepared for the upcoming hurricane season.

"Today's total power outage in Puerto Rico pinpoints the fact that we are still in a very fragile state. Moreover, the suffering of the Puerto Rican people seems to be nowhere nearing an end," she said.

Play ball!

But the mayor said backup systems and mobile tower lights allowed Wednesday night's baseball game between the Cleveland Indians and Minnesota Twins to go on as planned at Hiram Bithorn Stadium.

"Nothing will stop us," she tweeted.

Puerto Rico, home to more than 3 million US citizens, has grappled with widespread power outages for months since Hurricane Maria devastated the Caribbean island.

Puerto Rico's power outage is now the second-largest blackout in history

Puerto Rico has lost 3.4 billion customer-hours of electricity service due to Maria, according to an analysis released last week by the economic data analytics and policy firm Rhodium Group.

It's the largest blackout in US history (in terms of customer hours) and the second largest in the world -- after the outage caused when Typhoon Haiyan tore through the Philippines in 2013, killing more than 6,000 people.

Puerto Rico's power authority faced widespread criticism late last year for signing a $300 million contract to restore power with Whitefish Energy Holdings, a small Montana-based firm with only two employees at the time.

The utility canceled the contract amid public outcry, and its executive director stepped down in November.