Megan said a third person came "flying in like Superman" to try and free the woman.
By that stage the train driver had seen them and was desperately sounding the horn, which could be heard hundreds of metres away.
But the driver could not avoid the impact, which Megan said was "horrific".
She thought two of the rescuers managed to jump free. The woman who was helping had a bloodied knee but she didn't know if that was from the impact or falling to the ground.
The twisted remains of the wheelchair were visible under the train.
The train was blocking Morningside Drive, and Auckland Transport said one line remained blocked at the Morningside station.
Partial train services had resumed between Kingsland and Avondale, however people should expect significant delays.
Auckland police were investigating the incident.