A key road between Coppull and Standish has been closed for up to 10 days for emergency sewer repairs.
United Utilities had been working on A49 Preston Road to investigate damage to a sewer when they discovered it had collapsed this afternoon.
It affected the whole carriageway, so Preston Road had to be closed between the junction of Pepper Lane and The Olive Garden restaurant, in Standish.
The road is regularly used by drivers travelling to and from the M6 motorway.
Diversions are being put in place for motorists, who are advised to avoid the area.