Dramatic footage captured the moment two tourists were washed away by a flash flood before a brave onlooker leaps into the water to save them.

The two men were 'tubing' at a country park in Nakhon Nayok, Thailand, yesterday (August 13) when the heavens opened.

A sudden deluge of water swept them away downstream before they desperately clung to a low hanging branch.

Park worker, Khun Nalon, 40, was then seen plunging into the water on an inflatable ring to paddle after the stricken pair.

He caught up with them further downstream and helped to drag them to the shore.

Speaking after, Nalon said: ''I saw the men and was hoping they could hold onto the tree but then they let go.

''The water is very dangerous so they were not safe. I could not leave them. I am a good swimmer so I jumped in to help them.''

The Khao Yai National Park where the rescue happened is a popular nature reserve which was packed with locals who had the day off for a national holiday celebrating the country's annual Mother's Day.

Sudden monsoon downpours caused the streams to burst their banks - sending tonnes of water spilling over.

Hundreds of visitors were stranded in a resort inside the sprawling park with water levels too high for them to leave. They had to wait until evening when the water had subsided.

Park official Wichai Pornleesaengsuwan said the flash flood was caused by heavy rainfall coming down from the mountains.

He said: ''This is the worst flooding I have seen here for ten years. We are trying to ensure that everybody is safe and there are no injuries.''