Two protesters have abseiled down the Hataitai side of the Mt Victoria Tunnel in Wellington and hung a sign saying 'Restore passenger rail'.
Police have told the protesters they are considered trespassed.
More than a dozen police are on-site and motorists are being asked to avoid the area.
One of the protesters told RNZ they planned to lower themselves and their sign down over the road until it is closed.
Today's incident follows a number of protests on Wellington motorways last week.
A spokesperson for the Restore Passenger Rail group earlier said police were on site and traffic was still going through the tunnel.
He said two people were standing on top of the tunnel on the Hataitai side.
The tunnel is part of the central commuter route through the city.
