The in Lancashire is closed in both directions between J27 Shevington Interchange (Wigan, Parbold, Standish, Chorley A5209) and J28 Leyland Interchange (Leyland B5256) following a "serious incident", said on Sunday afternoon.
Emergency services, including Lancashire Police, North West Ambulance Service and a helicopter from North West Air Ambulance, were all sent to attend the scene, with the support of National Highways Traffic Officers.
The road closure, which National Highways said it's expected to continue for a "protracted period of time" to allow officials to carry out a full collision investigation, is promoting delays.
Lancashire police have issued an "avoid the area" warning this afternoon.
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