2 killed as helicopter crashes into crane in central London

London (CNN) -- A helicopter crashed into a construction crane atop a new luxury residential building in thick London fog Wednesday, killing the pilot and another person and sparking a line of flames as it plunged to the ground.

Thirteen others were injured in the crash that took place at the height of the morning rush hour in Vauxhall, south of the River Thames in central London.

One person was treated for a broken leg, but an ambulance service said the others were not seriously hurt.

"It is something of a miracle that this was not many, many times worse given the time of day," said police commander Neil Basu.

Vauxhall, not far from Westminster, is where a new U.S. Embassy is being built. The area, which is a mix of industrial, business and residential use, is also home to the headquarters of the UK intelligence service, MI6.

Neither of the two people killed have yet been named.

The pilot is thought to have been the only person on board the helicopter, which was on a scheduled commercial flight from Surrey, southwest of London, police said.

The second person killed "was in close proximity" to the helicopter, a London Ambulance Service spokeswoman said, but gave no more details.

Construction workers were at the site when the crash happened but were not hurt, she said.

James Whipps, a CNN producer, said the helicopter wreckage appeared to have landed on two cars by St. George Wharf, a major residential construction project.

Another eyewitness said rescuers pulled three injured people from two burning cars.

Thick smoke and flames billowed into the sky. The bent crane dangled from the building top, prompting police to cordon off roads in the area and evacuate residents and office workers.

The St. George Wharf construction project includes the landmark St. George Wharf Tower, also known as the Vauxhall Tower. Its developers, the Berkeley Group, say it will be one of Europe's tallest residential towers.

"I was standing outside having a cigarette when I saw the helicopter flying super fast towards the crane," said Rezart Islami, a builder who was working across the street from the 52-story building. "The pilot appeared not to have seen the crane because the helicopter hit it and went bang."

Islami said the rotor blade snapped off, and the copter spun to the ground and burst into flames."The top off the crane also came off in the impact," he said. "It all happened so fast, it was unbelievable."

Whipps said he heard the sound of the helicopter rotors suddenly cut out. He did not see the impact, but as he looked though a window, he "suddenly saw this enormous fireball, black smoke, shoot up from the side of a building."