The M53 motorway in the Wirral, Merseyside, will be closed for the rest of the day following the discovery of a body on the central reservation between junctions 2 and 3.
Merseyside Police said they received several reports of a body from passing motorists at around 7:15pm on Thursday 9 February.
Officers closed the southbound carriageway followed by the northbound to allow a search of the motorway, during which the body of a man was found.
The circumstances surrounding the man's death are still unknown, but police believe he was the victim of a road traffic collision.
No other casualties have been reported from the crash and police are now attempting to identify the man and inform his next of kin. A number of witnesses are assisting the police with their inquiries.
A Merseyside Police spokesperson added: "The M53 is likely to be closed in both directions for the rest of the evening and motorists are advised to check local travel reports before considering using the M53 in Wirral tomorrow morning.
"We would like to thank everyone affected by the motorway closure for their patience and understanding while police officers and the other agencies involved deal with this serious incident."