Flooding, debris and a slip near Paekakariki in Wellington is causing major problems for road and rail commuters this morning

State Highway One is closed to all southbound traffic just south of Paekakariki.

People coming into Wellington from the Kapiti Coast are being advised not to travel, or to expect long delays.

A detour's in place over Paekakariki Hill Road, but commuters have told Newstalk ZB there are slips on that road too.

Debris also fell onto the train tracks, causing a passenger train to derail early this morning, but there are no reports of injuries.

As a result, no trains are running between Plimmerton and Waikanae in either direction.

Meanwhile, services are suspended on the Johnsonville line between Wellington and Ngaio due to fallen trees south of Crofton Downs.