A man walked into Harpurhey Police Station with a grenade, after finding it in his allotment.
A cordon was put up along a section of Moston Lane after the member of the public strolled into the station with the device on Tuesday.
The incident happened just before 6pm and the road was closed off between Rochdale Road and Ashley Lane. No arrests have been made.
A spokeswoman for Greater Manchester Police said initial observations pointed to the device being a Second World War relic.
It's understood the device was moved to a location outside the station.
A 20-metre cordon was put in place but there were no evacuations as a result, GMP said.
Bomb disposals experts from the Royal Logistic Corps have been called to the scene, the spokesman added.
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An officer at the scene advised that anyone who finds a similar device is urged to contact police rather than move it themselves.
He said: "What we’d say is leave it in place and then call us.
"It could endanger other people."
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