AN Australian man is in a serious condition after he was attacked in a bathroom while out partying with his family at a nightclub on Thailand’s eastern Gulf overnight.

Police were called to Mixx Discotheque in South Pattaya, a popular resort city southeast of Bangkok, early on Thursday local time, after reports of a stabbing.

The victim, named by local media as 21-year-old Jaydon Sienkiewicz, was taken to hospital after being stabbed in the right side of his chest and is understood to be in a serious condition.

Jaydon, understood to be from the western suburbs of Sydney, was on holidays with family and friends.

The Bangkok Post reported Mr Sienkiewicz had been partying with a group of 10 people, including his Australian father and stepmother, and was stabbed while he was in the toilet.

His stepmother, Khumkhun Songnangrong, 33, reportedly told investigators they were having a “fun time” in the club and said she was not sure why anyone would stab her stepson.

She said she was horrified when he went to the bathroom and returned covered in blood.

In a statement to AAP, the Department of Foreign Affairs and Trade said it “stands ready to offer consular assistance to an Australian man hospitalised in Thailand”.

The club was closed immediately after the incident.

Police are examining CCTV footage from the venue to determine what happened, and it is believed they have interviewed the victim.