A slip has closed State Highway 2 on the Rimutaka Hill north of Wellington.

Police said in a statement at 8.30pm that the entire southbound lane was blocked at the bottom of the Featherson side of the hill.

"Traffic is already built up in the area as people travel back to Wellington from events in Wairarapa," the statement said.

Motorists were asked to be patient and to follow the advice of emergency services.