Motorists in the Royton and Chadderton area face further disruption, as essential sewer repair work will take longer to complete than planned due to the recent wet weather.
Street Bridge Road has been closed since February 15.
But United Utilities, which is carrying out the work, has confirmed that it needs to extend the road closure for a further two weeks - until 29 March - in order to "safely complete this essential work".
The water firm said in a statement this is due to the recent adverse weather which has hit the borough, including Storm Ciara and Storm Dennis, as well as the "close proximity of other services at the location".
A spokesperson for the water firm has apologised to local residents for the inconvenience and disruption that this will cause.
Work will be carried out between 8am and 8pm on weekdays and from 9am to 4pm on weekends. Pedestrian access will not be affected and a clearly signed diversion route will be in place for the duration of the work.
United Utilities say the work is part of an improvement project that the company is carrying out in Oldham, to future-proof its sewer network for the growing population of the town.