Deoki said St John is looking into what caused the vehicle to catch fire and is supporting those involved.
"We want to commend the actions of our first responder who acted quickly to secure the safety of those on board.
"We want to also acknowledge the support of our partners at Fire and Emergency NZ and Police who came to our aid."
Fire and Emergency shift manager Paul Radden said the alarm was raised at 8.45am and two high pressure delivery engines were sent to the scene.
Jon Reeves, a passenger on a Britomart bound train which stopped at the station, said the ambulance was "completely ablaze".
"[It] is actually pretty destroyed. Another ambulance has arrived and a police car."
Reeves said that when he passed the station the vehicle was still on fire and the fire service hadn't arrived.
"It is very unusual to see of course, and I just hope no one was inside."
Auckland Transport spokesman Mark Hannan said Otahuhu Bus station was evacuated due to the incident.
"All bus services are being diverted away from the station. Trains are not impacted at this stage," he said.
AT warned people to expect delays.
Police and FENZ gave clearance for buses and customers to re-enter Otahuhu Station at about 9.45am.
