Emergency crews were called to the popular boating location about 1.20pm on Saturday.

A 29-year-old woman has been transported by ambulance to Bendigo Health with burns to her face and arm.

She is a serious but stable condition.

Another 29-year old female suffered minor burns to her arm and right foot.

The 33-year-old male driver of the boat is believed to have suffered minor burns to his arm.

Xavier Sawford, 6, and his dad Jason were among the first on scene and used their fire extinguisher to help put out the flames.

"It just went boom,'' Xavier said.

His dad Jason, a Golden Square resident, said one of the women had jumped out of the boat screaming.

"We were parked next to them," he said.

"There was just a big loud bang and a big yellow flame went across the guy's whole boat, straight up her face and up the lady's leg.

"The flame just came up and covered them.

"I could hear him say, 'Oh, it's flooded', then he tried it again it went pop and it was just like woof, up she went.

"I ran over with the fire extinguisher.

"It ran out pretty quick but it got it out.

"Then we just threw a whole heap of water on it and kept it cool until the firies arrived."

Police have described the incident as a "mishap" and said there were no mechanical issues. 

It is believed the engine flooded and fumes were ignited.

"Just when they've tried to start the boat there's been a lot of fumes in the engine bay and it's just ignited," Leading Senior Constable Laurie Mueck said.

"The girls have just jumped into the water because obviously they've got a bit concerned about the burns.

"So they've kept themselves cool which was a good thing to do.

"There's no damage to the boat."