Rescue workers have freed the last of three crew members who were trapped in the wreckage of an SA Airlink plane that crashed outside Durban this morning.

Four people were critically injured when the aircraft went down in a school field shortly after takeoff, en route to Pietermaritzburg.

It has now emerged a woman who had been working on the school perimeter is among those injured.

SA Airlinks CEO Roger Vorster said an engine failure may have been to blame for the crash.

"We don't have the details of what caused the engine failure. The aircraft lost altitude, elected to do an emergency landing, ran out of runway... found a field at a school and attempted to land the aircraft on the field."

Comair bungle fixed

Meanwhile, Comair has said it has arranged an extra flight from OR Tambo Internation Airport to Cape Town at lunch time after an administrative bungle.

At least 20 people from Johannesburg were unable to board a Kulula.Com plan bound for the Mother City this morning.

It is still unclear why, but some passengers have told Eyewitness News the flight was overbooked.

The company's Gidon Novick said they have informed stranded travellers about the new flight.

"We still looking into it, whether there was an overbooking or another reason, it's not clear at this stage."