Eleven people face trespass related charges after a protest in Wellington, which delayed the demolition of a building in the path of the planned inner city bypass.

Several members of the Anti Bypass Action group have been arrested after chaining themselves to a roof-top balcony and inside rooms in the building off Vivian street.

Senior Sergeant Jason Ross says the police had to break through walls to get to four activists, who locked themselves against doors.

He says police went to considerable effort to reach the last two protesters and police were at the scene for about five hours.

Fulton Hogan says the demolition was not delayed by the protest action.

Public liaison officer for Fulton Hogan Sandra Ford says they are are concerned that the protesters are continuing to put themselves at risk with their actions. She says the level of security on the sites is under constant review.

Ford says the protesters were able to get on to the site because security was focused on another site where mechanical equipment was in use.

The protestors will appear in court next Friday.