Police have urged motorists to avoid the northbound carriageway of the M6 between Preston and Lancaster after a serious collision.
Officers have also advised drivers to ensure they have plenty of water and soft drinks if they get caught in long tailbacks caused by the smash.
At least one casualty has been airlifted to hospital following the collision which happened 10.45am today between junctions 33 and 34.
The northbound carriageway was completely blocked and traffic on the southbound carriageway was halted to enable an air ambulance to land on the highway.
Police say the helicopter has now left and vehicles have been released southbound.
One lane has since been opened on the northbound to allw trapped traffic to get past the scene of the collision.
But a spokesman said delays would inevitably continue long into the afternoon as work goes on to clear the debris and allow accident investigators to gather evidence.
“It is vital that anyone who may be caught up in the hold-ups has sufficient water or soft drinks in this hot weather.
“The queues are long and the vehicles stuck in them are likely to be there for quite a time.
“This is quite a serious road traffic collision and it will take a while to resolve it.”
Details of the collision are sketchy. Police say “at least one” casualty has been taken to hospital. There are no details at this stage about how many vehicles were involved.
By mid-day queues were stretching back to junction 31a at Fulwood.