Firefighters battling the SkyCity convention centre blaze are not using monsoon buckets, saying there's a risk to public safety dropping large amounts of water.
Former Westpac helicopter crewman Dave Greenberg said monsoon buckets carry between half a tonne and a tonne of water, and carrying loads like that could have a devastating impact.
"If one of the buckets dropped accidentally, which does happen, it could kill people on the ground or it could certainly damage things on the ground," he told The AM Show on Wednesday.
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Fire and Emergency New Zealand said due to the complex structure of SkyCity's roof, it wouldn't be effective to fight the fire with a helicopter.
"Helicopters with monsoon buckets are a firefighting tactic predominantly used for vegetation fires and very rarely used for building fires," they said in a statement.
By using aerial units and snorkels, firefighters are able to direct water to where it will be most effective.
"They'll be getting more water from all the snorkels they've got set up than they ever would from a bucket dropping 500 litres at a time," Dave Greenberg said.