LONDON (AP) -- A helicopter crashed into a crane and fell on a street in central London during rush hour Wednesday, sending black plumes of smoke into the air as it smashed into a crowded street. Two people were killed and nine others injured, officials said.

The helicopter crashed just south of the River Thames near the Underground and mainline train station at Vauxhall, and near the British spy agency MI6.

Police said one person had critical injuries. Several people were taken to a nearby hospital with "minor injuries," London Ambulance Service said.

The Ministry of Defense said it was not a military helicopter, and a British security official who spoke on condition of anonymity because he wasn't authorized to speak to the press said the incident was not terror-related.

The horrific scene unfolded at the height of the morning commute when thousands of pedestrians are trying to get to work.

Video on Sky News showed wreckage burning in a street, and black smoke in the area.  The video from the crash scene showed a line of flaming fuel and debris. Witnesses said the helicopter hit a crane atop a 50-story residential building, the St. George Wharf Tower.

Allen Crosbie, who works nearby, said the explosion convinced him and others that London was being attacked.

"I was 100 percent sure it was a terrorist attack," he said. "There was debris everywhere, a ton of black smoke. Parts of the crane, parts of the helicopter. I heard bang, bang, bang -- I presume it was the helicopter hitting the crane and then the ground. People were just panicking. Everyone thought it was a terrorist attack."

He and everyone just ran for their lives, he said.

William Belsey, 25, a landscape worker at the St. George Wharf Tower, said he heard the helicopter hit the crane.

"First we heard a big crash, looked up, that's when we saw the helicopter coming toward us. We heard an explosion as it hit the ground," he said.

Metropolitan Police Commissioner Bernard Hogan-Howe said he believed the helicopter was being diverted to a nearby heliport when it crashed.

"The top of the crane was actually obscured by fog so I didn't see the impact," Michael Gavin told the BBC. "But I heard a bang and saw the body of the helicopter falling to the ground along with pieces of the crane and then a large plume of smoke afterwards."

The area, roughly 10 blocks from the major Waterloo train and Underground station, is extremely congested during the morning rush hour. Many commuters arrive at the main line stations from London's southern suburbs and transfer to buses or trains there.

Aviation expert Chris Yates said that weather may have played a role. Investigators also would look at whether the crane had navigation lights.

"The question then becomes whether the pilot was fit," Yates said.