A 23-year-old Indian student, working as a taxi driver, was brutally stabbed and left bleeding on the roadside in Melbourne on Tuesday.

The Indian, who was lying injured for over two hours, was found at 6 am local time, disoriented and with hypothermia near a hotel in Clifton Hill, several hundred metres from his smashed car and was taken to hospital in a critical condition.

The victim, whose name has not been released, had stab wounds in the upper body and the homicide squad has been notified "as a precaution", the police said.

The Indian had apparently just started doing night shifts, driving the cabs. According to senior constable Brendan Smith, the suspect was possibly a passenger who might have driven the taxi a short distance after the attack, before it collided with a power pole.

Smith said the police were unclear of the motives and had not been able to talk to the victim due to his condition. "We are unclear of the motives. We believe there was one other person in the taxi," he said.

The Victoria police were reviewing CCTV footage from the taxi and have released photos that might help identify the attacker.

Taxi drivers blockaded a major intersection in central Melbourne to protest the incident. The secretary of the Victorian taxi drivers association, Pritam Singh Gill, said about 200 cabbies were blockading Swanston street to demand that all vehicles be fitted immediately with security screens.

"The drivers are very upset with this," he said. "The government promised us security and safety for the drivers more than 18 months ago and they haven't done anything so far," Gill said.

The police are also unsure whether the assault happened inside the taxi.

"We're discussing a couple of ideas at the moment as to what's occurred, but until we do establish what happened in the taxi, and obviously we haven't been able to speak to the driver because of his condition," Smith said.

Public Transport Minister Lynne Kosky described it as a very distressing incident and said the government is working on ways of improving taxi safety.