One police officer was examined by ambulance staff after decontamination and is not reporting any significant adverse symptoms. No other police or fire staff who underwent decontamination needed medical attention.
The Victoria St end of Chews Lane - a well-used pedestrian alley that houses cafes, a bar and apartments - is directly opposite the police and library buildings.
Detective Senior Sergeant Tim Leitch said police executed a search warrant after members of the public tipped them off to drugs at the address.
"The police kind of tripped upon this lab - we didn't realise there would be a lab there, so we weren't prepared for a lab."
Three people were arrested - two men and a woman - and decontaminated before being taken to the police station. Another man arrived while police were at the apartment.
"After a short foot chase he was apprehended. He's also been arrested and been brought back to the police station," Mr Leitch said.
Police were waiting for ESR scientists to arrive from Auckland to help assess the apartment.
Residents of some of the 95 apartments said they were evacuated about 7am - some two hours after the search warrant was executed.
Most residents are now back in the building apart from two apartments on either side of the scene.
Mr Leitch said the building had been evacuated in staged manner because police had not initially realised there would be a lab in the apartment.
"Because of the risk of potential fire and explosion, we had to evacuate the entire apartment block," he said.
One resident, Jonathan Kings, was surprised when told a drug lab had been found in his building.
He said nobody in the building had raised suspicions and the alleged offenders would have been "hiding in plain sight".
"I don't think of my apartment block as being home to clandestine labs - I think of them as being somewhere else."
Most residents were middle aged or elderly, with some families, Mr Kings said.
Police were less shocked by the find on their doorstop.
"I guess nothing really surprises me," Mr Leitch said.
"The labs can be very mobile - they can be set up pretty much anywhere. [There's] a lot of money involved with methamphetamine supply, a lot of profit, so I guess it's not surprising to find people setting up in a nice apartment."
Asked if the proximity to a police station was a bad look, Mr Leitch said: "I guess you could say that. I guess it just goes to show that they can anywhere, and police are certainly always keen to close these sorts of things down.
"My message would be if people see strange activity - if they hear activity or they smell chemical smells, running water, anything unusual - they should let us know because as you see, it could be anywhere.
"It could be anyone's next door neighbour that might be manufacturing meth."
It was not know how long the lab had been running for, Mr Leitch said.
The big dangers were explosion, fire and chemical contamination.
"There's significant risks involved with P labs."
