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
One of the victims of the Tunisia attack was Nottinghamshire social worker John Stollery, whose death has shocked the village of Walesby.
West Midlands Fire Service were called to a factory fire in West Bromwich last night but are still trying to determine the cause today.
A scattering of showers are likely this afternoon, a few of which could be quite heavy.