Sydney skatepark fire deemed accidental

A large fire at an indoor skatepark at Sydney's Olympic Park was accidentally caused by a welder doing repairs, police say.

It took about 70 firefighters to extinguish the blaze that broke out in the Monster Skatepark about 2.30pm on Friday.

A man aged in his 30s was hospitalised with minor smoke inhalation after the building was evacuated.

The fire was contained to the facility's indoor street-course, Monster Skatepark said on Facebook.

It remains closed but is working out when it can reopen for business.