Puerto Rico
The Puerto Rican flag flies near the Capitol building in San Juan, Puerto Rico. Joe Raedle/Getty Images

Most of the island of Puerto Rico was hit by a power outage early on Tuesday. More than 1.3 million people are in the dark.

Luma Energy said that it suffered a system-side blackout at around 5:30 a.m.

It said that while the cause of the outage is under investigation, preliminary findings point to a fault on an underground line.

It has activated emergency operations to restore power.

Luma says it will restore power to customers in phases but the full process will take between 24-48 hours.

Puerto Rico has chronic power outages that are blamed on a crumbling power grid, the Associated Press reported.

Hurricane Maria in 2017 caused widespread devastation to the power distribution system. It has struggled to completely rebuild it.