A man was lucky to escape his burning boat after it exploded in Sydney this morning.

The 34-year-old was left with burns to 30 per cent of his body after the vessel went up in flames on the Parramatta River, near the Iron Cove Bridge at Drummoyne.

He was on the deck when the blaze started about 8.45am, with a passing ferry pulling up alongside to douse the small boat with water.

Emergency services were called to the scene and paramedics treated the man before he was taken to Royal North Shore Hospital with serious leg burns.

He was said to be in a stable condition.

The cause is being investigated and the area has been contained to prevent oil from spreading.

It is believed to have ignited while the man was refuelling.

The boat has since sunk.