Police are investigating the accident on State Highway 5 near Rotorua, a popular destination for tourist groups from China, in which the bus flipped to the opposite side of the road on a "moderate to easy bend", an official said.

"It's a traumatic incident for all concerned, and it has far-reaching consequences," Brent Crowe, an inspector in the Bay of Plenty region, told a news conference.

Ethnic liaison officers were coordinating with victims' families and Chinese officials, he said, adding that police were working with the foreign ministry and the Chinese consulate to notify the next of kin.

An official at the Chinese embassy in Wellington told Reuters it was working with police to identify the victims.

Two of the injured suffered serious injuries, while four were less grievously hurt.