One person is critical and another seriously injured as police attend to multiple crashes overnight.

A three-car crash on the intersection of Great South Rd and East Tamaki Rd at 11.30pm last night closed the road for five hours.

"One person sustained critical injuries, two people moderate injuries and three minor injuries," a police spokeswoman said.

St John deployed two ambulance crews and a rapid response unit, and confirmed that one patient was transported to Starship Hospital in a critical condition.

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Then close to midnight, police were called to an incident on the Southern Motorway near Ellerslie.

"A person was seen running across the road on the motorway," the police spokeswoman said.

"The person was hit by a car and was reported to have serious injuries."

St John said two ambulance crews were sent to the incident at 11.55pm.

"We treated one patient in a serious condition and transported them to Auckland City Hospital," a St John spokeswoman said.

Police also received a few calls about a single mattress blocking the Northern Motorway near Northcote Pt at 11.30pm.

"We also received a call advising that a vehicle was driving along the motorway dragging a mattress behind," the spokeswoman said.

"It appears that it was stuck in the wheel and the vehicle had to pull over into a bus bay to remove it."

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She said police arranged for contractors to collect the mattress.

One patient was treated for minor injuries at the scene, St John said.