Motorists are stuck in traffic tailbacks because of the incident at Cow Lane's old bridge, which happened at 11.20am.
The Arnold Laver Timberworld lorry was travelling from Portman Road to Richfield Avenue when it became stuck. Police let down its tyres to remove it.
The road remains closed to motorists but is open for pedestrians and cyclists.
Network Rail spokeswoman Eimear Fitzpatrick said: "This is nothing to do with our project, but Network Rail staff are helping to clear the site so that we can get the traffic moving again as quickly as possible."
Engineers are on their way to the scene to check for any structural damage.
Updates to follow.