This is the dramatic moment hero bus passengers performed a citizen's arrest on an alleged pervert caught taking upskirt pictures in Thailand.

The students detained the middle-aged suspect, who they believed was using his phone to take photos under a young female passenger's skirt on September 11.

When the man tried to flee at the next stop in Samut Prakan, just outside Bangkok, the teenagers blocked his way and alerted the bus driver, who then slammed the doors shut and called the police.

Footage shows the brave youngsters pinning down the suspect and arguing with him as he asserted his innocence. However, when they seized his phone to check the files, they found several photos of the woman's underwear.

Officers later arrived to haul him to the police station.

Onlooker Too Winuktalop said: ‘On the way home, there was a commotion on the bus. At first, I thought it was just teenagers fighting, and I was about to leave. 

‘Then I heard one of the younger passengers shout, 'Close the door, this guy is a pervert! He secretly took photos under women's skirts'. The bus driver immediately stopped the bus, closed the doors, and went to see what was happening. 

‘He told the kids to stay calm while someone called the police. The bus was stopped as the younger passengers held the suspect down. He resisted and argued with them but the kids asked to see his phone, unlocked it, and gave it to the female victim to check. 

‘It turned out he really had been secretly taking photos and had sent them in a chat. The young woman took pictures as evidence. We don't know exactly when he took the photos.

‘The bus went from the Chamber of Commerce stop straight onto the expressway. At the first stop, the man tried to get off, but the boys blocked him and held him until the police arrived.'