A 42-year-old man died after being stabbed outside a Jalan Besar pub on Monday night, in a case that has been classified as murder.

Witnesses said Mr Chua Meng Guan had challenged his assailant to a fight before a scuffle broke out outside the pub and the hostel next to it.

He was later found on the floor, bleeding profusely from wounds on his chest and other parts of his body, where he was stabbed with a knife. His assailant was nowhere to be found.

Police said they received a call for help at 11.19pm. Mr Chua was pronounced dead at the hostel, called The Trey, about 10 minutes later.

No arrest had been made at press time. This is the third case of unnatural death in three days that the police are investigating, after deaths in Yishun and Geylang on Saturday.

Hostel manager Shammy, 36, who goes by one name, said he saw Mr Chua arguing with the assailant from the second floor of the hostel.

The man was shouting at Mr Chua, who was seated inside a black Toyota Camry, which was parked outside KSP Pub & KTV, Mr Shammy said.

Mr Shammy added that he saw the man holding something, which could have been a weapon. "It was wrapped in paper," he said.

The manager of the pub then intervened and separated the two men. He accompanied the assailant back into the pub. The assailant was wearing a black top and beige shorts, Mr Shammy added.

After that, the victim came out from the car and went to the pub, said Mr Shammy, who recognised him as a regular at the pub.

Mr Chua then came out, stood in the middle of the road and shouted out to the assailant, challenging him "to come over to the other side and fight", Mr Shammy said.

But the other man did not come out of the pub, he added.

Moments later, Mr Shammy heard a commotion and the sound of chairs toppling, and went downstairs to see what was going on.

When he reached the hostel entrance, he found Mr Chua wounded and bleeding. He also noticed that the man Mr Chua was fighting with had left. Mr Shammy tried to help the victim by putting pressure on his wound as the blood was "squirting" from the left side of his chest, he said.

A hostel guest called the police and another helped Mr Shammy by getting towels. "That's all I could do. I felt helpless," he said. "Within five minutes, he was dead."

A hostel guest managed to stop a passing police car but Mr Chua died before the ambulance arrived, said Mr Shammy.

Mr Joey Tan, 21, who works in a club, said he saw the victim go to the pub after challenging the assailant to a back-alley fight. Mr Tan, who was standing opposite the hostel at the time, said the victim tried to open the pub door but it was locked. He also heard the victim threatening to damage the assailant's car.

About 30 seconds later, the attacker came out, holding what appeared to be a fruit knife.

Mr Tan's friend, student Josephine Leung, 25, said she saw the two men brawling before Mr Chua got stabbed.

Mr Chua was walking away from the pub, she said, when his attacker shoved a table at him. He pushed it away, and the attacker shoved it at him a second time. He then fell and that was when the assailant stabbed him and fled, she said.

A 55-year-old man, who wanted to be known only as Ah Huat, said he was eating at a nearby stall when he saw the victim getting stabbed thrice - in the chest, arm and leg.

The unemployed man added that the suspect went back into the pub and fled through the back door.

Chinese evening daily Lianhe Wanbao reported that Mr Chua was heard shouting in Hokkien: "Yes, I owe you money, but we are brothers. Is there a need to use a weapon?"

Speaking to The Straits Times, Ms Angeline Lim, 60, the wife of one of the pub's owners, said neither the suspect nor the victim were members of its staff.