Emergency services have been stood down from an Auckland office building where two suspected gas leaks sent 14 people to hospital yesterday.

People were rushed to Auckland City Hospital complaining of nausea and shortness of breath after four floors of the Augusta Building on Victoria St West in central Auckland were evacuated about 9am yesterday.

Three more people were taken to hospital with mystery illnesses about 5.30pm after another unexplained suspected gas leak.

Fire and Emergency assistant area commander Dave Woon said last night firefighters along with the Defence Force used specialised equipment to try to detect any hazardous substances, but they could not find anything.

This morning they had handed the incident over to the property owner and had notified WorkSafe and the Auckland Regional Public Health Service.

The building was placed in lockdown last night, but now the situation had been handed over to the property owner, Woon said,

"[It is] for them to make a call as to whether it is reopened or not."

A spokesman for the building had not responded to requests for comment this morning.

Last night the spokesman said the landlord and building manager would be assisting Auckland Regional Public Health Service and WorkSafe with an investigation into the incident.

Preliminary testing carried out by FENZ, Police and the New Zealand Defence Force had not identified the source of the smell, he said.

"Subsequent oxygen tests are normal with zero pollutants identified in the contamination testing."

Tenants initially evacuated the building as a precaution after the first incident, and the building had been cleared for re-entry before the second callout.

Qantas said several people at its office in the building had become unwell after fumes became apparent about 9am.

A spokesman for the company said Qantas would be investigating - but that the focus was on the welfare of the affected employees.

"Emergency services attended the scene and a number of people were taken to hospital in a stable condition," he said.

"They are our first concern and we are monitoring their progress."