Shocking footage shows armed officers carrying out a raid in Barking Road at around 2pm this afternoon.
One video showed armed police aiming their weapons towards the roof of a parade of businesses.
They can be heard shouting: "Stand up, show us your hands."
Another shows a man running along a roof.
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Armed police appearing to aim their weapons towards a first floor window
Shocked witnesses said the raid by a Paddypower branch was "absolutely terrifying".
Malik Rouf, 30, said one of the men inside the flat jumped out of a first floor window on to a ledge before he was pulled back inside.
A still from a video showing a man on the roof of a parade of shops with armed police below
He said: "He was about 30 years old and in a vest – he tried to go out the window but the officer was standing with a gun saying 'get back in, get back in'.
"He was dragged out and put in a police van."
Shimma Ali, 32, said it was terrifying to see dozens of armed officers in the street.
She said: "I heard a woman screaming and 20 officers with guns – there was a sniper across the road trained on the window.
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"They were shouting 'we will shoot you if you don't go back in'.
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Police at the scene in Barking Road, east London
"I thought he was going to get shot – the police officer had his gun on him and was ready to shoot."
"It's absolutely terrifying – we don't expect it in this area, it's so multicultural and diverse, there's no racism."
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Armed police responding to the incident at London Bridge
Social media users have described the chaotic scene on Twitter.
One Twitter user said: "Avoid Barking Road high street North area. Police anti terror raid. Full on lock down."
Another said: "Madness on East Ham Barking Road."
A third Twitter user said: "Please, if anyone is in & around the East Ham area at the moment – Be Safe. Armed Police & Police Vans have cordoned off the High Street."
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Unmarked police cars blocking off Barking Road
While it has not been confirmed if the incidents are related, it comes after police raided a home in Barking believed to be linked to last night's London Bridge and Borough Market terror attack.
Seven people were killed, along with three terrorists, after a van and knife attack.
And yesterday a separate incident saw Barking Road sealed off by police investigating an incident which left two officers injured.
This is a developing story. More to follow…