Armed police are searching a home in Surrey following the arrest of a teenage suspect linked to the attack on a Tube train.
Residents in the Cavendish Road area of Sunbury-on-Thames have been evacuated from their homes as operations continue.
A spokesperson for the Metropolitan Police said the “precautionary measure” was taken as officers search a house linked to an 18-year-old suspect arrested in Dover earlier on Saturday.
The arrest was described as “significant” by the Met, who previously suggested they were searching for more than one suspect.
“Cordons are being put in place at a 100-metre radius to facilitate the Metropolitan Police operation, which is being supported by colleagues from Surrey Police,” a spokesperson said.
“A search of the address is ongoing and the cordons will remain in place until the operation is complete. No further arrests have been made.”
Neighbours in the leafy suburban town expressed shock over the operation, which started at 1.40pm.
Steph Forsyth told The Independent she could see the ongoing raid from her window, adding: “It’s outside a house and there are lots of police cars and dogs.”
Images showed residents gathered at a police cordon, with police thanking them for their “cooperation and patience”.
Mojgan Jamali, who lives in Cavendish Road, said police knocked on the door and told her she had “one minute” to pack her bags, grab her children and leave her home.
The mother-of-three told the Press Association: “I just got out, I got my three children and we left the house and the street.
“We didn’t know what was going on. There was a lot of rumours going on, a lot of stories, people saying this and that, but we didn’t know.
“Earlier the police came around and asked if we could look after another family in our home for a little while, which I was obviously happy to do.
“But then they came back later and just said we had one minute... I hope this gets settled soon, that we can get back to normal.”
It came as the Government’s emergency Cobra committee met for a second time in the wake of the Parsons Green attack.
Amber Rudd, the Home Secretary, said Saturday’s arrest was “very significant” but would not give any further information on the suspect’s alleged role.
“Police have made good progress,” she added. “There is no doubt that this was a serious IED and it was good fortune it did so little damage, although we are of course sympathetic to the people affected by it.
“We will have to make sure we take all the steps we can to ensure that the materials this man was able to collect become more and more difficult to combine together.”
Investigators are believed to have identified the person who placed the bomb on a District Line train during Friday morning’s rush hour using CCTV footage.
It partially detonated at Parsons Green station, injuring 29 people, but officials said the main explosives failed.
Theresa May announced that the national terror threat level had been increased to “critical” overnight, meaning further attacks are considered imminent.
Armed police and soldiers have been deployed to guard key sites amid continued threats by Isis, which claimed responsibility for the attempted bombing in a statement saying it was launched by “soldiers of the caliphate”.