A passenger was dragged 600m under a bus in central Wellington before the driver realised anything was wrong, the Tramways Union says.
Emergency services were called to Taranaki St just before 10pm on Saturday after the pedestrian was killed in the incident.
Cordons were put in place and motorists were asked to avoid the Taranaki St area between Ghuznee St and Bidwill St.
Police spent the night examining the scene and the road didn't reopen until the following morning.
A police spokesperson said it was "quite a significant" crash scene in terms of the size of the area and it took some time to process.
Tramways Union Wellington secretary Kevin O'Sullivan said he has spoken to the driver involved.
"The driver is still in quite a state of shock."
O'Sullivan said the pedestrian was actually a passenger on the bus who got off at a stop outside Massey University.
The driver told him the passenger got off the bus and was clear of the vehicle before he shut the door.
It wasn't until the driver came to a stop further down the road at the intersection of Vivian and Taranaki Streets when he felt a "bump", O'Sullivan said.
"He then discovered what had happened, but prior to that he had no inclination at all that anything was wrong."
The distance between the bus stop and the intersection is about 600 meters.
O'Sullivan said the bus involved has been impounded and the driver wouldn't be back at work for at least a few days yet.
Police said this afternoon the investigation into the circumstances of the crash was ongoing and no further updates were available.
NZ Bus has been approached for comment.
A Greater Wellington Regional Council spokesperson yesterday confirmed the vehicle involved was a Metlink bus, but said they could not provide further details as the matter was with police.