Chinese tourists have told consular officials the bus they were in was travelling fast before it collided with a car in Otira Gorge, injuring 16 people.
Investigators will pore over the remains of the bus and a car that were involved in a catastrophic crash at the gorge on Thursday.
The crash injured many Chinese tourists on the bus as well as the three Swiss occupants of the car with which it collided.
A total of 36 tourists were involved in the collision, which left many trapped and at least 16 injured.
Two of the nine people who remain in Christchurch Hospital are Swiss, one of whom is in a critical condition and the other is stable.
A Chinese consular official said he spoke to someone who could only remember that the bus was travelling fast.
Nick Li said three family members arrive from Shanghai tonight.
He is hoping to speak to the rest of the passengers by the end of today.
Police said their investigation was continuing and the Serious Crash Unit was pouring over the vehicles looking for any mechanical defects.
Senior sergeant Stu Koefoed of the Tasman Command Centre in Nelson said both vehicles had been impounded and were being examined for mechanical defects by the Serious Crash Unit at Greymouth police station.
The driver of the bus is a New Zealander who will be spoken to by police in due course, he said.
Police will also be speaking to the Swiss nationals who were in the car, but they cannot do so at this stage because of their injuries, as well as the Chinese nationals who were in the bus.
There did not seem to have been anything wrong with the road at the time of the crash and there was nothing at this stage to indicate either of the drivers were on the wrong side of the road when the accident happened, Mr Koefoed said.
The crash was described by an ambulance official in charge of rescue operations as the biggest one he had attended.