|The unexploded German WWII bomb weighs 250kg. Pic: West Midlands Ambulance Service|
The Aston Expressway is expected to be closed until Tuesday morning as the German shell, which weighs up to 250kg (551lbs), is removed from a nearby construction site.
Hundreds of homes and businesses within a 500-metre area have also been evacuated, and West Midlands Police says the cordon may have to be widened.
|A digger is transported to the construction site. Pic: Central Motorway Police Group|
Birmingham Police Commander Chris Johnson said: "There have been some difficulties in accessing the device given the terrain and its position within a construction site.
"All agencies involved are working as quickly as possible to bring the situation to a safe conclusion with brave military staff risking their safety to ensure that of the public."
Highways England says all entry and exit slip roads at Junction 6 of the M6, which connects the motorway to Birmingham city centre, have been closed.
The agency has "strongly urged" road users to consider alternative routes, and to allow additional time for their journeys.
London Midland says all rail services between Birmingham New Street and Lichfield, Staffordshire, have also been cancelled.