Counties Manukau Fire Service assistant area commander Craig Monrad said police removed drug paraphernalia including a syringe and prescription medications from the area where the man had become unwell.
The man said he'd been injecting morphine, said Mr Monrad.
No other substances or chemicals were located.
Auckland Council manager environmental health Mervyn Chetty this morning said hazardous substances response officers had not received a request for assistance from the police or fire services.
Middlemore Hospital spokeswoman Lauren Young said the man was in a stable condition at Middlemore Hospital this afternoon. He declined to speak to media.
Westfield parent company Scentre Group today said the safety of its retailers, customers and staff "remains a priority".
"Any potential threat is treated seriously," it said.
"We have strong working relationships with all agencies to ensure the on going safety of shoppers and retailers.
"All incidents are reviewed and assessed for any possible changes to procedures."
