Dozens of city centre workers were forced to leave their offices yesterday so police could comb a Birmingham square for clues on a stabbing.
A 23-year-old man was knifed in the chest in St Paul's Square after he tried to escape a gang of robbers.
The victim was fighting for his life in intensive care at a Birmingham hospital last night.
He had been walking home through St Paul's Square with a friend at 1.45am yesterday when the gang of three teenagers pounced in what is believed to have been an attempted robbery.
During the scuffle a knife was produced and plunged into the victim's chest. The gang then fled and an alarm was raised.
The victim's friend, who was in his 20s, was not injured. Police sealed off the area and carried out a search.
The first gang member was described as about 17, of chubby build, with short Afro hair.
He wore a light-grey tracksuit with a hooded top, a black baseball cap and white trainers.
The second is aged about 16, about 5ft 8in, of slight build and wore a black tracksuit with a hood which featured a red logo. He also had a black cap. The third attacker is aged between 16 and 17.
A West Midlands Police spokeswoman said: "This was a brutal attack and we would like to hear from anyone who may have seen this gang in the area late last night or early today."
Witnesses or anyone with information can call police on 0845 113 5000.