MIAMI, Florida (CNN) -- A "significant equipment failure" at a substation west of Miami triggered Tuesday afternoon's blackouts around southern Florida, a Florida Power & Light official said.
Motorists try to navigate an intersection in southern Florida after traffic lights went out.
Utility spokeswoman Aletha Player said an investigation is ongoing, and provided no details of the failure. But she said the 700,000 customers affected by the outage in southern Florida should have power restored by 5:30 p.m.
Outages were reported from Miami to Jacksonville on Florida's east coast and as far north as Tampa on the Gulf Coast, police and utility officials said.
The outage occurred shortly after 1 p.m., the company said.
A strong cold front and scattered thunderstorms moved through the region, including one that prompted a tornado warning for Fort Lauderdale, the National Weather Service reported. But a National Weather Service meteorologist told the southern Florida-based Sun-Sentinel that there were no major storms in the area at the time electricity went out that would cause such a large failure.
"We are looking at a number of scenarios," said FP&L spokeswoman Karen Vissepo. "We are in a restoration mode. We are restoring power to those who were affected. We are doing it in a systematic fashion, restoring power by areas."
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Mike Stone, a Florida Department of Emergency Management spokesman, said 2 million to 3 million people were affected. Power began returning to many of those areas within an hour and a half, officials reported.
In Washington, officials at the Department of Homeland Security said there was no immediate concern that terrorism was behind the outage.
Stan Johnson, a spokesman for the North American Electric Reliability Council, said eight power plants were off-line across the region.
He said that officials believe the outage has been contained.
Both nuclear units at the Turkey Point power plant in Miami-Dade County were off-line as of about 2:30 p.m., Florida Power & Light nuclear-plant spokeswoman April Schilpp told the Palm Beach Post.
The units shut down after off-site power to the plants was halted, Schilpp told the Post. Another Miami-Dade County power plant, which isn't nuclear, also lost power, the Post reported Schilpp as saying.
Detective Robert Williams, a Miami-Dade County police spokesman, said power was out across the entire county within 20 minutes of the outage. The blackouts extended into neighboring Broward County, which includes Fort Lauderdale, and north to Palm Beach County -- a region of about 6 million people.
Miami International Airport, which has emergency generators, reported only brief delays. Schools remained in session during the blackout, said Cmdr. Charles Hurley, a spokesman for the Miami-Dade school system's police department. And Delrish Moss, a county police spokesman, said no major traffic problems had been reported.
In Palm Beach County, spotty outages ranged from Riviera Beach to Boca Raton, said sheriff's spokeswoman Teri Barbera.
The Orlando Sentinel is reporting that local schools, businesses and intersections are without power Tuesday afternoon.
According to the Orlando newspaper, about 7,000 customers of Kissimmee Utility Authority lost power for about 20 minutes Tuesday.
Tampa Electric spokeswoman Laura Duda said about 50,000 customers lost power at the outset of the blackouts, but for all but 2,000 customers the lights were back on within an hour. And central Florida's Progress Energy reported all but 30,000 customers of the 150,000 initially affected were still without power by mid-afternoon, most of them in the Tampa Bay area.
