The tank measured 15-20m high, and they were prepared to assist with retrieval and access.
The Ruakākā Volunteer Fire Brigade, with Whangārei crews, responded as the callout was initially thought to be related to a hazardous substance.
However, it was shortly afterwards determined to be a medical event.
Hato Hone St John sent a rapid response unit and ambulance.
The Northern Rescue Helicopter spokesman said when they arrived, access to the worker had already been established.
Two critical care paramedics were lowered by winch at a nearby roadway, and the helicopter landed at a designated spot near the port.
The paramedics joined Hato Hone St John to provide advanced medical care.
The man was airlifted to Whangārei Hospital in a critical condition.
WorkSafe is not investigating, as the emergency was because of a medical event rather than a workplace accident.
Brodie Stone covers crime and emergency for the Northern Advocate. She has spent most of her life in Whangārei and is passionate about delving into issues that matter to Northlanders and beyond.