MIAMI, Florida (CNN) -- Power 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.

As many 800,000 Florida Power & Light Co. customers are without power Tuesday afternoon, the company said.

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.

The outage struck shortly after 1 p.m. ET. 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 the cause of the outage was not immediately known.

National Weather Service meteorologist Barry Baxter told the South 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.

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, Schlipp 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.

In Palm Beach County, spotty outages ranged from Riviera Beach to Boca Raton, said sheriff's spokeswoman Teri Barbera.

Outages stretched into neighboring Broward County, which includes Fort Lauderdale, he said.

Dade, Broward and Palm Beach counties are home to nearly 6 million people.

The Orlando Sentinel is reporting that local schools, businesses and intersections are without powerTuesday afternoon.

According to the Orlando newspaper, about 7,000 customers of Kissimmee Utility Authority lost power for about 20 minutes Tuesday.