Many parts of southern Florida were blacked out on Tuesday afternoon, leaving two to three million residents without electricity.

Florida Power & Light said a failure at one of its substations starting shortly after 1 p.m. caused other parts of its system to shut down to protect the integrity of the electrical grid. The utility said most of its customers should have their power back on by 5:30 p.m.

The failure first occurred at Turkey Point nuclear station just south of Miami, according to the Florida Division of Emergency management. The division also provided the figures for total blackout victims.

As of 4 p.m. about 800,000 people remained without power, according to state officials. Areas affected include stretches from Miami to Jacksonville in the east. The loss of power stretched as far north as Tampa and the Gulf Coast, authorities said.

Officials said they were systematically restoring power to the region.