The A49 Wigan Lane is closed in both directions, with queuing traffic, due to an accident involving a lorry.
The incident has occurred between A5106 Chorley Road, near the Boar's Head, and Elmfield Road.
There is congestion to Standish town centre and severe delays throughout Wigan town centre as traffic tries to divert the closure.
There are also minor delays through Red Rock.
The road was fully closed at 5pm after a generator fell from a lorry and caught fire.
The road had been blocked for ten minutes prior.
Transport for Greater Manchester have urged for people to avoid the area and seek an alternative route.
A spokesperson for Greater Manchester Fire and Rescue Service said: "At 3.30pm this afternoon as were called to a road traffic collision on Wigan Road.
"A generator has fallen from a moving lorry and landed on the road obstructing traffic, igniting a fire and releasing battery acid.
"Nobody was injured in the collision.
"To protect the environment we have covered the drains in the area and used dry powder to extinguish the fire.
"We have used highly absorbent soda ash, sand and oil absorbent powder to prevent the battery acid from harming the local environment.
"As of 6.30pm this evening we have made the scene safe and handed over to the police."
