The M6 northbound near Preston ground to a halt tonight after a lorry overturned.
The incident happened between junction 31a (Longridge) and junction 32 for Broughton.
North West Motorway Police tweeted: "We are taking reports of a RTC on the M6 NB J31a - J32.
"Patrols are making their way but at the moment traffic has come to a stop at J31A from CCTV.
"Pls consider alternative route if you are heading this way this evening and we will keep you updated."
The North West Air Ambulance was seen landing.
A lorry was believed to be on its side.
One motorist said: "People are out of their cars. It looks like we are to be here for a long time."
Traffic was backing up towards Leyland and Walton Summit.
And later police closed the southbound carriageway.
Lancashire police tweeted at around 6.30pm: "Following a serious RTC on the M6 northbound, the southbound carriageway will be closed temporarily from J32 whilst we deal with the incident."