(CNN) -- A massive outage has wiped out power to Puerto Rico's capital San Juan.
The problem is with a failure on a main north-south transmission line, said Fernando Padilla, an official with the Puerto Rico Electric Power Authority, known as PREPA.
"It was a mechanical issue on the line, could have happened at any line," he said. "It's being patrolled and repaired by PREPA."
Power went out about 11:30 a.m. local time (10:30 a.m. ET).
Homes and businesses that had been on grid power had to restart generators if they had them.
Marianne Sanchez told CNN her Rio Piedras neighborhood got power back just six days ago. She wrote on Instagram, "This is a not too friendly reminder of how fragile our power system is."
Power generation plummeted from over 40% of capacity to 18% on Thursday, PREPA said.
Much of Puerto Rico has been without power since Hurricane Maria smashed the island on September 20.