This is the astonishing moment a knife-wielding taxi driver chased a tourist over an alleged fare dispute in Thailand.

The holidaymaker reportedly hailed the Thai motorcycle taxi driver through an online app, but refused to pay the fare upon arriving at his destination in 'Sin City' Pattaya, on February 21.

Dramatic dashcam footage shows the backpacker sprinting across the motorway as the helmet-wearing cabbie ran after him brandishing a knife.

The passenger dashed across the median strip and was able to shake off the alleged attacker.

Nam, 30, a female motorist driving behind the pair, said: 'Before the incident, I was traveling to the Sattahip District.

'When I arrived at the scene, I saw a Thai motorcycle rider trying to chase after a foreign man while holding a knife in his hand. The tourist ran for his life across the road.

'I honked at them because I was worried other cars would run them over. I drove away after that. I don't know what caused their fight.'

Non, 56, a security guard who works at a nearby building, said he had heard the pair arguing in the middle of the road.

He added: 'I couldn't hear them clearly but I think they were fighting over the fare. The taxi driver was screaming that the foreigner had cheated him.'

Police said no complaints were filed about the knife attack.

Former fishing village Pattaya became popular with American troops on 'rest and relaxation' breaks in the 1950s and 1960s when the U.S. military had bases in Thailand while fighting Communism in Vietnam. Rural families are said to have even dressed their sons as women to cash in on the gold rush.

The handful of bars in the coastal town quickly grew and it is now the world's biggest sex holiday destination, with round-the-clock prostitution and drugs - a modern-day Sodom and Gomorrah rife with crime and debauchery.

Government chiefs have attempted to clean up the city but regular violence, depravity and claims of corruption continue to blight its reputation.