An air ambulance landed on the motorway following the incident in the southbound carriageway between the M25 and Junction 9 (Gatwick Airport).
According to reports, three cars and a motorbike were involved in the collision at about 2pm.
The road has now been closed both ways due to the incident between Junctions 8 and 9 near Gatwick.
Diversion for both directions can be found on the Highways England website m.highwaysengland.co.uk/#news
Highways England said in a statement: “Our officers are working on getting road users caught in the closures clear of the motorway as soon as possible.”
Police, paramedics, and the fire service are on scene.
Surrey Road Police said: “We’re are currently attending a serious collision on the M23.
“The motorway is CLOSED in BOTH directions between Junction 6 and 7.
“As a result there is an extensive amount of traffic in the area.”
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