A miles-long stretch of the M66 is expected to be closed all morning and into the afternoon after a car struck a woman's body on the motorway.
The M66 northbound has been shut between junctions 1 and 3 in Bury, Greater Manchester, while police investigate the incident.
Officers were called just before 2am on Thursday to reports that a car had collided with a body in the northbound lanes.
Emergency services attended the scene and found the body of a woman.
Police are now trying to establish how the woman ended up on the motorway.
It was unclear whether the woman was already dead when she was struck by the car.
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The motorway closure isn't likely to be lifted until the afternoon, and motorists are advised to follow the detours in place, said Highways England.
Drivers and bus passengers were facing delays of more than an hour, with seven miles of slow-moving traffic in the southbound lanes towards Manchester.
A spokesperson for Greater Manchester Police said: "Investigative work is currently being carried out on the M66 following a collision.
"Shortly after 2am this morning (Thursday), police were called to reports that a car had collided with a body on the M66 northbound in Bury.
"Emergency services attended and sadly found the body of a woman.
"Enquiries are ongoing to establish how the woman came to be in the carriageway.
"The M66 northbound is currently closed from junction 1 to 3.
"Please avoid the area where possible."
Anyone with information about the incident is asked to contact Greater Manchester Police or Crimestoppers.
