The owner of the travel company whose bus overturned on an icy Southland road on Thursday says it's a first for the 15-year-old business.

Four people were seriously injured on Thursday morning and another 11 received moderate to minor injuries when the tourist bus crashed on the Mossburn-Te Anau Highway, or State Highway 94, about 4km north of Mossburn.

The coach, operated by Worldway Travel and carrying 30 people, had been travelling behind another bus at about 40-50km/h when it hit the ice, spun 180 degrees and went off the road backwards, landing on its side and hitting a power pole.

Worldway Travel manager Jason Yu said there had been no serious crashes since the company launched in New Zealand in 1997.

"For the big bus this is the first time," he told NZ Newswire.

"We really are keen to know what happened."

Mr Yu said the company ran a South Island bus tour once a week and the bus was into its third day of its journey when it crashed.

He said the company catered for Chinese-speaking people from China and resident in New Zealand and it was likely there was a mix of New Zealand and Chinese residents aboard the bus when it crashed.

Three helicopters flew to the scene and took three people to Southland Hospital with serious injuries.

One woman had a fractured ankle, a second woman had chest, shoulder and neck pain, and a 55-year-old man had chest and back pain.

A nine-year-old boy with abdominal injuries was flown to Dunedin Hospital with his mother.

The bus driver was also taken to Southland Hospital as a precaution, while 10 others suffered moderate or minor injuries.

Police are talking to the Chinese consulate in Christchurch.

The crash knocked out power to the local area, but it had since been restored.