Pirate monkeys attacked a boat full of tourists to snatch food from them.

The cheeky primates swam across the river and climbed the boat before grabbing a bag of snacks from a holidaymaker's hand at the Kaeng Krachan National Park in Phetchaburi province, Thailand, on July 30.

Footage shows the aggressive macaque leading its troop by fighting a woman for her colourful, starchy crackers, which she had to throw into the water to stop the others from coming.

The troop of adult and baby monkeys then waded into the water to take the food while stuffing some into their mouths.

One of the sightseers Kaewlin Ketkaew said: 'Our trip to Kaeng Krachan almost became a disaster. It was my first time stopping by to feed the monkeys and it was so chaotic.'

Monkeys in Thailand have become accustomed to tourists feeding them, and they will often become aggressive. They have also been known to steal food and belongings from tourists.