The southbound carriageway of the A3(M) has reopened after an earlier incident, but the northbound carriageway remains closed between the A27 near Havant and junction 3.
Drivers are being warned of delays after reports of people in the road, that saw both north and south carriageways closed to traffic this morning
According to traffic monitoring service Inrix, police are at the scene of the incident on the northbound carriageway between junctions J4 at the Purbrook Interchange and J3 for Cosham.
In a statement a spokesperson for Hampshire Police said: "We are currently dealing with a serious incident on the A3(M) between junctions 4 and 3.
"As an update, the southbound carriageway has now reopened but the northbound carriageway remains closed.
"It is likely to remain closed for some time while the emergency services deal with the incident.
"Please avoid the area if you can.
"Thank you for your patience."