A accident on the Royal Windsor Way, formerly known as the Windsor relief road, is causing long delays in the town and the surrounding area.
Twitter users are reporting traffic is at a standstill, with the road closed heading in the Slough direction.
One user, Sophia Swain, said people were out of their cars and traffic was 'gridlocked' in the area.
Another user, Andrew F, said traffic is ok heading away from Slough, but the Clarence Road roundabout is at a near standstill.
Police are on the scene.
An accident on the M4 westbound between junctions 8/9 and 10 is also reported as having a knock-on effect on surrounding roads.
Updates to follow.
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