Loughborough MP Nicky Morgan says she "heard an almighty bang" and "saw clouds of thick black smoke" as the helicopter crashed into a crane in South London this morning.
The MP was walking towards Vauxhall tube station, when the accident happened.
"Ms Morgan says she "saw clouds and clouds of thick black smoke billowing from the ground" and that initial thoughts were that a bomb had exploded."
More top news
Generally cloudy with fairly persistent rain through this evening.
A cloudy evening, with sporadic outbreaks of rain or drizzle. These will ease away overnight, with a few clear spells around dawn.
The House of Commons Petitions Committee has said they will keep an eye on the petition and are concerned about fraudulent signatures.