A Vietnamese man who suffered serious injuries, following the freak accident in which an 80 kilo loose truck wheel hit the bus he was travelling in on Auckland's Southern Motorway, has died in Auckland Hospital.

The wheel came off while the truck was travelling south near Mt Wellington yesterday, and hit a bus on the other side of the motorway.

The man, who is in his 20s, suffered serious brain damage while three other people suffered minor injuries.

Family members had gathered at his bedside before turning off his life support.

The passenger was in the front seat of the bus near the driver. The wheel injured three other passengers in the bus, none seriously.

Sergeant Stu Kearns said it was too soon to say if charges relating to the man's death would be laid.

"It's a little bit early to make that call but we will have to just see once the inspections and the various people have been spoken to.

"It's a possibility yes, but it's a bit early to say," he said.

Mr Kearns said the truck was being inspected by mechanical experts today and further consideration of issues, including charges, would continue on Monday.