The collision is just before Junction 2 heading northbound and has caused a large backlog of traffic and congestion towards J1.
A lorry, two cars and a van are believed to have been involved in he crash.
Nationonal Highways said the M18 is closed closed in both directions between J1 and J2 – between Bramley near Rotherham and Wadworth near Doncaster.
The agency added: “Closure due to a very serious collision. South Yorkshire Police-led incident.”
National Highways added: “This closure is due to a very serious collision. South Yorkshire Police are in attendance.
“It is anticipated that the road will remain closed until at least 11pm tonight for a full investigation to take place.
“Delays are building on the approach, with approximately three miles of congestion and 20 minute delays above normal in both directions.
“Traffic is being diverted.”
Northbound motorists should follow the hollow triangle symbol via the A631 westbound towards Rotherham, A6021, A6123 and A630 northbound to the A1M J36 at Warmsworth.
Southbound motorists follow the hollow diamond symbol – via the above route – but roads in reverse order.
Delays are likely on the diversion routes.
South Yorkshire Fire and Rescue said: “A multi-vehicle non bus RTC has potentially closed to the M18 North between the M1 and M18 J1.
“Severe delays are expected in the Aston and Tinsley areas.”