It is understood that one of the students was so scared he demanded to be let off at the nearby settlement of Dobson.
The bus, carrying high school and junior school students from the Greymouth area home to Totara Flat, northeast of town, then started swerving on the road and slowed considerably.
The Ritchies bus driver, Peter Brown, said he suddenly became "crook as a dog" and needed the help of two teenagers to shift the gears and work the handbrake.
"I was sick as anything and I needed them to come help me and they did - full credit to them, they were excellent," Mr Brown said.
Mr Brown said he was feeling very ill that morning but went to work. That afternoon, he became so sick it seriously impaired his driving ability.
Seventeen-year-old Nadine Lawton and another Greymouth senior student went to the front of the bus and saw Mr Brown needed their help controlling the bus.
The other Greymouth student helped Mr Brown change gears while the driver worked the clutch.
When they were able to pull over to the side of the road, Miss Lawton pulled up the handbrake for the driver.
Mr Brown did not go into detail about why he needed the students' help, but said: "They just knew. They could see I needed them. They really were excellent."
Miss Lawton's mother, Fiona, said her daughter had her full driving licence, and the two senior students could tell the driver needed help.
She said her daughter had to guide the driver and tell him how to drive.
"He wasn't driving well and was clipping things and driving into things, so they went and guided him. They all stayed very calm," said Mrs Lawton, whose 12-year-old son Cameron was also on the bus.
"They were lucky though, it could have been a lot worse. If he knew he was sick, he shouldn't have been driving."
Mr Brown said he had been checked by a doctor and was waiting for his medical assessment.
Ritchies managing director Andrew Ritchie said the matter was being investigated and Mr Brown had been stood down until the company received his medical results.
"We want to make sure we're fair to this guy and don't hang him out to dry. We're just gathering exactly what happened."
The students on board yesterday met at Greymouth High School and gave written statements to police.
Grant Soeters, whose 15-year-old daughter was on the bus ride, said the incident yesterday was the last straw.
"He's just obviously past it - [having] an 82-year-old bus driver is insane," he said.
"There have been many other incidents as well. This is definitely not the first time something like this has happened."
Mr Ritchie last night defended the employment of an 82-year-old bus driver.
"I don't make the laws, I don't decide how old is too old. He had his licence up to date and had passed all the tests - that's all we need."
The NZ Transport Agency requires bus drivers to have a valid licence with a passenger endorsement to be road legal.
All drivers have medical assessments at 75, 80, and every two years thereafter.
A spokesman for the Ministry of Education said it required school bus drivers to have medical tests each year regardless of age.
The rules
Bus driver requirements:
* Valid driver's licence.
* A passenger endorsement.
* Medical assessments at 75 and 80.
* Medical assessments every two years over 80.
* The Ministry of Education requires school bus drivers to have medical assessments every year.
- additional reporting, APNZ
