ONE man is dead and fourteen others have been hospitalised with suspected drug overdoses at a music festival in Penrith, Sydney yesterday.

The 23-year-old deceased reveller travelled to the Defqon.1 festival by car with several friends.

Just before midday he was taken in to the festival's medical tent, where his condition quickly deteriorated and he suffered several seizures, police say.

An ambulance was then called and took the man to Nepean Hospital where he was resuscitated numerous times after multiple cardiac arrests.

He died at 10.30pm last night.

A police spokesman told The Daily Telegraph they were unsure what substance the man had consumed.

"That information is being prepared for the coroner," he said.

"It is certainly a warning to others out there if it was an overdose, which is what it is looking like."

Over 18,000 people descended on the Sydney International Regatta Centre yesterday to listen to a range of hardstyle dance music.

A police operation with drug dogs nabbed 87 partygoers, three for public order offences and the remainder for drug offences.

An attendee took to Twitter saying the death may have been associated with a bad batch of ecstasy pills. Police have not confirmed this allegation.

Defqon. 1 Festival is an annual music festival held in the Netherlands and Australia. It was founded in 2003 by festival organiser Q-dance and plays mostly hardstyle and related genres such as hardcore techno, jumpstyle and hard trance. Many prominent hardstyle and dubstyle artists perform there annually.

Police have announced a media conference regarding the man's death and the large number of arrests made at the event for this afternoon.

They also warned users of illegal drugs to be aware that while they may believe they are purchasing one drug they may get something completely different.

"People who attend dance parties and music festivals need to act with caution when considering taking an illicit drug. The effects of some of the more popular drugs at these venues such as MDMA (ecstasy) can cause overheating and dehydration with sometimes fatal consequences," Penrith Local Area Command Crime Manager Detective Inspector Grant Healey warned.

It was the fifth year for the event described as being for "hard dance enthusiasts" with tickets for the Sydney International Regatta Centre event costing as much as $235.

On its website organisers stress "This festival is produced to give everyone a positive and safe experience. Q-dance maintains a zero tolerance drug policy. There will be a strong police presence at the event."

Headline acts include Coone, Gunz for Hire, Frontliner and Brennan Heart.