Fire service personnel move a man to a waiting ambulance outside Femme Fatale gentleman's club in Central Auckland.

Two people rushed to hospital from an Auckland brothel had taken the class B drug GHB, police say.

The pair were transported to Auckland Hospital from Femme Fatale gentlemen's club on Wellesley St at 8.30 on Saturday morning.

They were a woman in critical condition and a man in serious condition, St John Ambulance spokesman Robbie Walker said.

JASON DORDAY/FAIRFAX NZ Emergency services outside Femme Fatale on Wellesley St West.

A police spokesperson said the male patient told police the pair had taken Gamma-Hydroxybutyrate or GHB, a drug also known as "Liquid Ecstasy".

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GHB is a central nervous system depressant popular with club goers because it provides a euphoric high, increased sex drive and a feeling of tranquillity. However, it has numerous side effects including sweating, loss of consciousness, vomiting and hallucinations. A 2002 study found 69 per cent of GHB users reported losing consciousness.

Colourless and odourless, GHB is also used as a date rape drug. It is particularly dangerous and potentially fatal if mixed with alcohol.

Auckland Hospital said both patients from Saturday's incident at Femme Fatale were in a stable condition.

An eyewitness at the scene saw one patient, a man, writhing around on a stretcher as he was transported to a waiting ambulance.

A woman who answered the club's phone said she had "nothing to say".

Femme Fatale bills itself as "New Zealand's #1 gentlemans club" and offers massages and an escort service.