One person has been airlifted to hospital in a critical condition following a crash in the central North Island which left five others injured, too.

Police expect State Highway 1 at Waitahanui, south of Taupo, to be reopened by 10pm following a serious crash around 5:30pm.

After initial reports that six people were injured, two of them seriously, it can be confirmed that one person has now be flown to Waikato Hospital in a critical condition.

The five others suffered "lesser injuries," according to police in a statement.

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The crash has caused lengthy delays to motorists using the busy stretch of road.

"Motorists are asked to remain patient and take care when passing the scene."

"Police are aware that a total closure of the highway involves a lengthy detour around the western side of the lake and will endeavour to keep the highway partially open," a spokesperson said after the crash.

The serious crash unit is investigating.