The Port of Auckland's container terminal will remain closed until at least tomorrow after a worker was critically hurt when a straddle truck tipped over.

Emergency services rushed to the scene on Ferguson Wharf about 3.45am.

The man was extracted from the truck and taken to Auckland Hospital. He is in a critical condition.

St John Ambulance said in a tweet it attended an incident on the waterfront at 3.46am.

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Port of Auckland acting chief executive officer Wayne Thompson said at this stage they did not know the cause of the incident.

"Our primary concern is for the welfare of our colleague and we are doing everything we can to look after him and his whānau, friends and colleagues," Thompson said.

A full investigation was under way and the container terminal would remain closed until at least 7am tomorrow.

Police said WorkSafe was investigating.