"I think everyone left after last night, people put their plans on hold and waited until this morning [because of the weather] which was a good decision."
Southern police communications Shift Inspector Rick Dury said traffic was heavy in and out of Christchurch, both to the north and south.
"Unfortunately due to the weather it is moving slowly, as is appropriate to the conditions ..."
Police appealed to the public for patience, Mr Dury said.
Some roads in the Oamaru region had also been closed as storm conditions from ex-tropical cyclone Ita moved south, he said.
Meanwhile, State Highway 36 from Rotorua to Tauranga remains closed due to a slip.
Police said roading contractors are working to clear the road, however it is expected the road will be closed for most of the day.
Traffic can divert at Ngongotaha to State Highway 5 and across the Kaimai Range or travel through Rotorua CBD to State Highway 33 toward Te Puke.
Motorists were advised to avoid the area.