Yibeth Morales told Newshub the trouble started when a new driver took over the bus.

"The driver was saying he didn't know how to drive a manual, so he was just getting told how to drive a manual in that moment by the driver we had before," Morales said.

"He just fell to the ground, shaking his head. His legs were shaking. [He] started vomiting, started spewing in the bush."

She said at the first intersection, he couldn't stop the bus and it was "really bad".

The driver pulled over while stressed and panicked.

Morales said he sat outside and rubbed his head with his hands while sweating and crying.

But things got worse on his second driving attempt, which ended on the side of the road, again.

Morales said the second time was bad and he started crying and "freaking out".

A passenger offered to drive, but he wasn't allowed to.

When the bus stopped again, police and an ambulance turned up.

InterCity wouldn't comment on the incident, but it's understood the passenger who briefly took over driving was a qualified bus driver.

A company driver was then sent to complete the journey to Auckland, which arrived after 1am and without several passengers who got off in Rotorua.

Morales said she doesn't blame the driver, who she felt was under pressure to continue driving.

"It was really unfair for him and we were so worried for him," she said.

But her attempts to get answers about why they were put at risk have so far gone unanswered.