Army disposal experts will work overnight to defuse an unexploded bomb, meaning 150 people will be forced to spend the night in a school hall.
The Second World War bomb was discovered by contractors at a building site in east London at around 12.45pm on Monday afternoon, leading to evacuations of houses and businesses and the introduction of a 100-metre police hazard zone.
Ministry of Defence (MoD) experts arrived at Temple Street, Bethnal Green, at around 5pm to defuse the 250kg device and are expected to be working through the night.
Tower Hamlets council has set up a rest centre in a nearby school and arranged emergency beds for all the residents affected.
An MoD spokesman said: "We can confirm that a specialist military bomb disposal team from 11 EOD Regiment, Royal Logistics Corps are on site in Bethnal Green and are assisting the police with the ongoing incident involving a WWII German aircraft bomb that was discovered earlier today."
Several roads remain closed as police warned of "significant traffic disruption" and Transport for London (TfL) said there was no impact to Tube or overground services, but four bus routes are being diverted.
Police have advised motorists to avoid several roads including: Old Bethnal Green Road, Warner Place, Squarres Street, Bethnal Green Road, Cambridge Heath Road and Hackney Road.
A Tower Hamlets spokesman said: "We are taking the advice of the Metropolitan Police and London Fire Brigade and will follow the council's Emergency Planning procedure to ensure residents and visitors to the borough are kept safe.
"Residents and visitors are advised to avoid this area. We have set up a rest centre in a local school with a full Rest Centre Team en route to the school."