NEW YORK CITY ? A huge power blackout hit U.S. cities spreading from New York to Cleveland and Detroit and north into Canada Thursday afternoon.

In New York City, the blackout affected subways, elevators and airports, including John F. Kennedy and LaGuardia airports.

Thousands of people streamed into the streets of lower Manhattan in 90-degree heat.

In Toronto, Ontario, too, workers left their offices after the blackout hit shortly after 4 p.m. EDT.

Traffic lights were out throughout downtown Cleveland, creating havoc at the beginning of rush hour.

There were reports of outages in New Jersey and Connecticut as well.

Every prison in New York state reported a loss of power and had switched to backup generators, said James Flateau, a spokesman for the state Department of Corrections.

White House officials were monitoring the blackout from Washington and from San Diego, where President Bush addressed troops at midday.