London's fire brigade says it is attending to a helicopter crash near the Thames river in the central part of the city.
News reports say the aircraft crashed into a crane before hurtling to the ground, sending plumes of smoke into the sky. The helicopter is believed to have hit two cars, jamming traffic in the southern part of the city during the morning rush hour.
Reports say the crash happened near Vauxhall Station, one of the main junctions for rail traffic entering the city. It is not clear whether there are any casualties.