Two men remain fighting for life after reaction to unidentified substance at Queensland house party

Two men remain seriously ill in hospital after an apparent drug overdose suspected of killing a third reveller at a huge party on the Queensland-NSW border.

Police have fast-tracked testing of a suspicious substance after some of about 500 revellers fell ill at a Mount Lindesay party that attracted about 500 revellers on New Year's Day.

Emergency services were called to the address in Mount Lindesay about 10.20am on New Year's Day after several people became ill.

Within minutes, one young man was dead and two others who came forward with symptoms soon went into cardiac arrest.

They were airlifted to hospital in critical condition.

They all had an "adverse reaction from an as-yet unidentified substance", police said.

The two survivors were flown to Gold Coast University Hospital and Toowoomba Base Hospital.

There were believed to be up to 500 partygoers at the secluded Ubunye festival on Hardgrave Road.

Detectives are investigating the incident and will prepare a report for the coroner.