Rakaia Bridge on State Highway 1 has reopened following a serious crash this morning.

Emergency services attended the crash, which closed the bridge and caused traffic to back up.

Motorists are asked to take care on the bridge and in the surrounding area, and to allow for further delays near Ashburton, where a road rebuild began today.

A single lane is operating on SH1 south of Tinwald, with road users required to stop on demand.