A three-vehicle crash 30 minutes north of Christchurch has blocked State Highway One.

The crash near Mill Road, Leithfield in the Hurunui District was reported around 12.20pm.

One person is in a serious condition and three people are in a moderate condition, police said.

The Serious Crash Unit has been advised.

A three-vehicle crash on State Highway 1 near Mill Road, Leithfield has blocked the road and left one person seriously injured. Photo / George Heard

Hato Hone St John said it was notified of a motor vehicle incident on Ashworths Rd in Leithfield at 12.18pm.

Emergency services are on the scene at the crash near Leithfield. Photo / George Heard

“We are currently on the scene with three ambulances, one rapid response vehicle and an operations manager,” a spokeswoman said.

“Our paramedics have treated one patient in a serious condition who is now being transported to Christchurch Hospital.”

The road is blocked and diversions are in place; motorists are advised to expect delays.