Television images showed two people in a minivan climbing into a basket that was lowered from a helicopter flying overhead. A boat also was being used as rescuers attempted to reach motorists in the frigid water.

Montgomery County fire department spokesman Pete Piringer said at least a dozen people had been rescued from their vehicles as crews struggled with the swift water to reach more cars. No injuries were reported.

Authorities said it was a 66-inch (168-centimetre) water pipe that broke on River Road near the Congressional Country Club in Bethesda.

Morning temperatures in the area were well below freezing. -- AP