UPDATED 11.08AM: A unit on the roof of Pastoral House in downtown Wellington has caught fire and caused chaos in the inner city.

Office workers have poured onto the Terrace as smoke billows from the building behind TVNZ and Les Mills.

Fire shift manager Chris Dalton said they have crews up on the roof controlling the fire.

He said it looks more spectacular than it actually is, but reached second alarm level so extra trucks have been brought in to fight it.