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.
Megan said she couldn't believe what she'd just seen.
"I just sat in the car for a minute saying, 'Did that really happen?'"
The twisted remains of the wheelchair were visible under the train.
Some people who saw the incident were too shocked to speak and were being comforted by Victim Support.
One man fought back tears as he recalled the desperate attempts to free the woman. He didn't know how the woman had been stuck on the tracks and watched in horror as the rescuers shook the wheelchair to try to free her.
The train was blocking Morningside Drive, and Auckland Transport said one line remained blocked at the Morningside station.
Partial train services have resumed between Kingsland and Avondale, however people should expect significant delays.
Auckland police were investigating the incident.
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- With nzherald.co.nz