Two men whose images were captured by a surveillance camera are being sought by police investigating the suspected arson attack in a popular Mong Kok market street on Wednesday that killed nine people. Their blurred photographs were issued by police last night as five of the 34 people injured in the Fa Yuen Street blaze remained in critical condition in hospital. Eleven are in stable condition. A senior police officer said a reward of HK$300,000 or more might be offered to people providing information about the early-morning fire that started in market stalls and spread to nearby flats. The men were filmed walking separately in the space of about five minutes at the junction of Fa Yuen Street and Bute Street about the time the fire broke out. 'The two men may provide important information to us so we want to interview them,' said Superintendent Brian Lowcock of Kowloon West regional crime unit in appealing for help. 'At this stage, we are not treating them as suspects.' Chief Executive Donald Tsang Yam-kuen said if it was arson, the person responsible would be caught. 'We must take swift action to catch the perpetrator,' he said. He also promised to conduct a thorough investigation into the cause of death of the nine victims in the city's deadliest fire for 15 years. Police have identified eight of the dead - two men and six women. Many residents were trapped as two lines of hawker booths on each side of Fa Yuen Street caught fire at the same time, at about 4.40am on Wednesday, cutting off exits and creating billowing dense smoke that poured up staircases into six blocks of flats. More than 300 firefighters took about eight hours to douse the flames and rescue trapped residents. The nine victims were found collapsed on the staircase of an eight-storey tenement at 192 and 194 Fa Yuen Street. The building had two stairways, with one at the back leading to another street. But survivors said they did not have access to the back stairway or did not know about it. One man, a tenant of one of four cubicles in a subdivided sixth-floor flat, said he was the only one who had access to the back staircase and used it to escape. An inter-departmental working group chaired by the chief secretary was set up to investigate the cause of the blaze, offer help to residents and improve public safety. 'Making no improvement is unacceptable,' Tsang said. Among solutions discussed at a meeting between officials and two hawker associations yesterday was dismantling market stalls after trading hours, which provoked a hostile reaction from traders. Last night, more than 300 affected residents were still not allowed to return home as the six buildings remained cordoned off by police. Some of them stayed in shelters in Mong Kok and Yau Ma Tei. Police said it would take another day for them to finish examining the site. Anyone with key information on the fire is urged to call police on 9022 0072 or 2761 2344.