The Indian city of Calcutta has been remembering the victims of last Friday\'s devastating hospital fire, which claimed 90 lives. West Bengal Chief Minister Mamata Banerjee led the mourners in paying respects to those who died. Ms Banerjee said her government would take steps to ensure such an incident would not happen again. The fire began in a basement and swept through the AMRI hospital. Most of the dead were patients. All of those who died suffered asphyxiation, post-mortem examinations said. Six directors of the hospital, considered one of Calcutta\'s most prestigious, have been arrested and charged with culpable homicide. Officials said the hospital did not meet safety regulations. A memorial has been erected at Subroto park near the hospital and floral tributes were paid to the victims on Monday. A police band played in remembrance. \"We must take steps to prevent recurrence of such a tragedy. I will sit with all my departments and ensure that,\" Ms Banerjee told the gathering. More remembrance rallies are scheduled to be held later on Monday. The BBC\'s Amitabha Bhattasali in Calcutta says the chief minister will also help 36 residents of a nearby slum who risked their lives to help out the rescue. The youths went into the building to save patients before the fire engines arrived, our correspondent says. The bodies of two nurses who died trying to save patients have been flown back to their home state of Kerala. Chief Minister Oommen Chandy attended their arrival and said PK Vineetha and Remya Rajappan would be afforded state honours at their burial. The fire started in the basement of the hospital and spread throughout the six-storey building. Police and fire officials say the basement was supposed to be a car park but it had been turned into a warehouse where highly inflammable materials were stored. An investigation has revealed that the fire services were not called until almost two hours after hospital staff noticed the blaze. Local residents, firefighters and some hospital staff managed to save about 50 patients. Officials said fire alarms, sprinklers and firefighting equipment were not working in the hospital - charges denied by hospital authorities. The government has ordered a judicial inquiry into the incident. Those charged include the co-founders of the hospital SK Todi and RS Goenka. The licence of the hospital has been cancelled. Fires in high-rise buildings are fairly common in Calcutta. There have been at least 10 major incidents since 2008, with electrical short circuits mostly responsible.