Auckland's ninth and final Police checkpoint is up and running on State Highway at the Bombay Hills, but traffic is building as Aucklanders head south.

NZME reporter Will Trafford is at the Mill Rd checkpoint.

He says about 10 Police officers and six Defence Force members are stopping and questioning all southbound drivers about where they are going, and why.

He says motorists could be turned around, if their reason isn't valid.

"We have seen many campervans and vans which have been stopped, which left officers rather sceptical as they talked to some of these people."

Trafford says there are significant delays from the Mill Rd checkpoint at the Bombay Hills.

"They're essentially taking all the southbound traffic off and questioning them on Mill Road about where they are going."