Techno ravers flash the flesh with some VERY skimpy outfits as they party in furnace-like conditions in Sydney - after notorious face-tattooed bikie's throat is SLASHED at Perth gig

Thousands of concertgoers have turned out to party at techno rave Epik despite a sweltering heatwave while a major bikie figure was stabbed at another festival. 

More than 20,000 people have descended on Sydney's Olympic Park on Saturday for several concerts.

Ravers were seen rocking up in colourful outfits with some wearing revealing dresses as they prepared to party long into the night at the electronic dance festival

The dance music event at Sydney Showground is among several concerts lighting up Olympic precinct. 

US rockers Foo Fighters will play to a huge crowd at Accor Stadium while rapper 50 Cent will also get thousands jumping at his second Sydney show at Qudos Bank Arena, despite the stifling heat. 

Earlier NSW Health issued a fact sheet urging concertgoers to try to avoid the sun and to take a break from dancing if they feel unwell.

The mercury reached 42C on Saturday afternoon in Homebush where the concerts are being staged. 

The factsheet warned people not to consume alcohol or drugs while attending the events as this can have a particularly bad affect during a heatwave. 

A cool change is expected to sweep through Sydney tonight with strong wind gusts of up to 90km/h predicted to provide much needed relief for late night revellers.

'If you're dancing outdoors and or taking MDMA it can be very easy to overheat as the drug interrupts your body's cooling down mechanism, meaning your body will create more heat than it can get rid of,' the factsheet read. 

NSW Health Minister Ryan Park said the government had been working with the organisers of the events in Western Sydney and was happy with preparations.

'We've worked with organisers to make sure that there is free water available and plenty of water available to those attending those music festivals,' Mr Park said. 

Paramedics are on alert as the concerts get underway with a 20 per cent increase in distress calls being recorded across the NSW Ambulance service on Saturday. 

NSW Chief Superintendent Mark Gibbs said the ambulance service has been coping with the increasing number of calls throughout the day and urged concertgoers to keep themselves and each other safe. 

'We ask the community to keep an eye out for vulnerable members of the community,' he said, encouraging attendees of the festivals to hydrate, wear light clothing, and use sun protection,' he told the Daily Telegraph. 

As the concerts swing into full gear, one of Australia most notorious bikies Dayne Brajkovich was stabbed during a brawl outside a Perth music festival on Friday night. 

Brajkovich was allegedly stabbed in the neck at the event as festivalgoers were leaving the Ministry of Sound Classic at Kings Parks in the city's CBD.

He was rushed to hospital and was discharged on Saturday morning with his fingers  taped up with bandages following the  alleged incident.