Police suspect three Chinese men have left the country after kidnapping a female Chinese university student and then killing her when they failed to obtain a 2.5-million-baht ransom from her father in China.

Police said on Sunday that the body of the Chinese student was found in a ditch in Bang Yai district of Nonthaburi on Saturday afternoon.

The body was in a sack and had about five stab wounds in the left side of her chest, along with a wide stab wound in her right shoulder.

Surveillance camera footage showed three Chinese men abducted the 22-year-old Chinese woman. identified as Jin Can, from Bangkokthonburi University last Tuesday. They brought her in a Mazda car to a rented house in a housing estate in Bang Yai and held her there.

Detectives learned that gang then used the WeChat application to demand a ransom of 500,000 yuan, about 2.5 million baht, from her father in China.

The father received the ransom demand together with a picture of his daughter with her wrists and ankles tied. He then asked the university about his daughter's whereabouts.

The university told the father that his daughter was last seen at the university between 5pm and 7pm last Tuesday.

They believed it was a prank, so the father did not transfer the ransom to the Bank of China. Later, the father became concerned when he was unable to contact his daughter.

Surveillance camera footage showed the three Chinese men arriving in the red Mazda car at 1.30am last Wednesday near the location where the body was found.

The Chinese men left the rented house at 3pm on Wednesday. The vehicle was returned to the rental company in Bangkok on Thursday, the day the three men left for Chengdu.