Two people died a helicopter crashed in central London after it clipped a large construction crane. Security officials say there is no indication of any terrorist involvement.
The helicopter crashed in the city's southwestern district of Wandsworth, close to Vauxhall train station, at about 8 a.m. local time on Wednesday.
London police confirmed that two people had died in the incident, with two others taken to hospital.
Witnesses said the helicopter first hit the crane and then crashed some 400 meters (1,300 feet) away.
"There was a massive explosion. People were shouting and screaming," on eyewitness told the BBC. Another said he had seen the aircraft burst into flames before hitting the ground.
Security officials at London's Counterterrorism Command said there was "nothing to suggest any terrorist link."
It is unclear whether the helicopter was a commercial or private aircraft. Britain's Department of Transport said air accident investigators were on their way to the site. Visibility was reported to have been low in the city on Wednesday morning. Unconfirmed reports said the helicopter was an Augusta 109.
Fireball, plume of smoke
Fire crews were said to be at the site of the crane, which was said to be in a "precarious position."
A large plume of black smoke was seen rising from the fireball surrounding the wreckage. Police widened a cordon around the crash scene due to reports of leaking gas in the area.
It is believed the crane was constructing the 181-metre Vauxhall Tower. When built, the tower will be the tallest residential building in Britain.
Helicopters routinely follow the length of the River Thames when navigating across London.
rc/ipj (AFP, AP, Reuters, dpa)