Florida Power & Light still does not know how a glitch at a substation triggered a blackout that cut power to millions across south Florida. The power outage affected millions of people as it snarled traffic at intersections and trapped residents in elevators across the state.

The outage, which affected at least 2 million people, according to a Reuters report, was controlled relatively swiftly, and power came back to most areas of the state within several hours.

Armando Olivera, president of Florida Power & Light, said the afternoon blackout was triggered by an unexplained equipment failure and fire at a Miami transmission facility, which caused an automatic emergency shutdown of the Turkey Point nuclear plant in south Florida.

"We will conduct an extensive investigation into all aspects of the failure," Olivera told reporters.

According to the Associated Press, sporadic outages Tuesday spanned 300 miles of the peninsula but appeared to be concentrated in the southeast portion of the state. Communities along the southwest coast, in the Florida Keys and as far north as Daytona Beach reported interruptions.

Florida Power & Light spokeswoman Amy Brunjes said today that the utility can't say whether it will be days or weeks before the explanation for the blackout is found, the AP report said.

Olivera said an equipment malfunction at one electrical substation should not have caused the outages. "None of the events should have caused the kind of widespread outage that we saw," Olivera said. "That's the part that we don't have an answer for yet."

The AP presented the following timeline:

At about 1 p.m. an equipment malfunction happened at a facility that transmits power in Miami, starting a sequence of events that caused power to go off in areas around the state. A switch failed, like a short circuit, and a fire broke out at the facility, which in turn caused larger problems — disabling two power distribution lines between Miami and Daytona Beach, according to FPL. Systems monitoring the power grid saw took action, automatically shutting down two nuclear plants at the Turkey Point facility south of Miami. A fossil fuel plant also went off-line.