A long section of motorway between Rochdale and Oldham has been closed due to a 'police-led incident'.
No further details have been revealed.
Paramedics, however, are at the scene together with police.
National Highways said the A627M is currently closed in both directions.
Motorists have been advised to avoid the area.
Witnesses at the scene said police Tactical Aid Unit officers were also present.
National Highways said the southbound carriageway was closed between junction three for the M62 and junction one, at Elk Mill Retail Park in Oldham.
The northbound carriageway is also closed between junction one and two, Slattocks roundabout.
The Manchester Evening News has asked Greater Manchester Police for more details.
Police were seen earlier at a tunnel under the A627M off Hough Lane, which runs underneath the motorway between farms.
National Highways said: "Emergency services including the North West Motorway Police Group are in attendance.
"Highways England has resources deployed to assist.
"Road users are advised to expect disruption and to allow extra journey time."
A diversion is in force.
National Highways added: "Road users wishing to travel southbound are advised to travel westbound on the M62 to J18 then join the M60 clockwise to J21.
"Travelling northbound on the A663 turn left at the A669 junction (Middleton Road) and join the A669 westbound. Remain on the A669 to its junction with the A664.
"At the roundabout join the A664 northbound (Assheton Way). At the next roundabout continue north on the A664.
"Remain on the A664 (Rochdale Road) to the Slattocks Roundabout/A627M junction. Join the A627M Slattocks Link to then re-join the A627M northbound."
No further details have been revealed.
