Terrace Tunnel stand-off ends after nearly 10 hours

A man who was on top of Wellington's Terrace Tunnel since a head-on collision early this afternoon has come down and been arrested after nearly 10 hours of negotiation with police.

The 31-year-old man was standing on a row of large metal pipes running above the tunnel since it was closed in both directions following a two-car crash just after 12.30pm.

He came down at about 10.30pm after speaking to a family member.

Wellington District Commander Inspector Chris Bensemann said more than 20 police staff - including AOS, police negotiators and dog teams - assisted and all possible tactical options were considered.

"In the end this became a matter of patience and communication and we are glad the incident was resolved without further injury," said Inspector Bensemann.

"I would also like to thank Fire and Emergency NZ, Wellington Free Ambulance, and Metlink for their assistance in hot and tiring conditions throughout the nearly 11-hour incident.

"We are aware of the major disruption this caused to traffic around the city and police would like to again thank the public for their patience and understanding."

The man is currently in custody, where he will be medically assessed. No information is available on possible charges.

Earlier, police said he had a knife with him and was struggling with personal issues.

Mr Bensemann said the man's health deteriorated in the sun throughout the afternoon, but he had since perked up and was refusing water.

"This is very much a game of patience, where we have to wait for him to come down."

Mr Bensemann said the man had requested to talk to his partner.

Four double decker buses were parked underneath underneath the man to reduce the drop space.

NZTA advised people all afternoon to use an alternate route, or delay travel.

Southbound traffic was forced to use the Terrace offramp onto the The Terrace and northbound traffic was redirected along Willis Street, The Terrace, Everton Terrace and onto the Clifton onramp.