Police launched a murder investigation into the deaths of eight men after the blaze, which broke out at the private Dream City club just before 6pm on Saturday.
They want to trace a man seen with a red petrol can who later ran empty- handed towards Farringdon railway station. He was about 20, white, with short dark hair and is believed to have been wearing a dark jacket with a light fleck, dark trousers and black shoes.
A local resident who helped the injured said she heard two men saying someone had fallen down the club stairs after being punched and had returned for revenge. A local garage employee said he sold a petrol can to a man who filled it from a pump.
Detective Superintendent John Chaplin said the blaze, described by a senior firefighter as the worst he had seen, appeared to have started in the entrance of the four-storey building in St John Street, near Smithfield Market. Sixteen men suffered serious injuries. Last night seven were critical.
Dream City showed straight and gay sex films and occupied the second and third floors. Witnesses said flames engulfed all floors within minutes of the building 'exploding'. The injured suffered severe burns, broken bones and the effects of smoke inhalation. Some jumped from third-floor windows. The pavement outside became strewn with dead and injured as police and ambulancemen battled to revive badly burned victims.
'They were bringing people outside, laying them down and trying to resuscitate them, pumping their chests,' said Valerie Martin, who lives near by. She added people could not escape because the fire had begun in the main hallway.
Peter Cook, a removal man working near by, saved one middle-aged man before firemen arrived by backing a lorry up against the building. He said the trapped were hysterical as they scrambled to escape.
Ken Emsley, station commander at Euston, said: 'It was a horrific incident. The worst I have experienced in 30 years. It was absolutely chaotic. We were working under extreme conditions, with so many people trying to get out of the building.'
Efforts to escape may have been hampered by a lack of lighting. One man who had been inside said the cinema was 'very dark and very seedy'. Islington council said yesterday that the club was not licensed as a cinema. The owner has been traced and was being interviewed by police.
Last night post-mortem examinations showed seven died from smoke inhalation and one from multiple injuries consistent with a fall from a window. Mr Chaplin hoped to name the dead once the next of kin had been told.