A major explosion caused by a gas leak flattened two residential buildings in Manhattan on Wednesday, killing two women and injuring 24 people as thick white smoke billowed into the sky. New York Mayor Bill de Blasio called the incident "a tragedy of the worst kind" and raised concerns about a number of people still unaccounted for after the disaster in East Harlem. The explosion sparked inevitable reminders for some New Yorkers of the 9/11 terror attacks in 2001 that brought down the Twin Towers. Other witnesses said it felt like an earthquake. There were 15 apartments in the two buildings that collapsed, de Blasio and city officials told reporters near the scene at 116th Street and Park Avenue, a mainly Latino community. Around 15 minutes before the blast, energy company Con Edison received a call from an adjoining apartment building alerting maintenance staff to the smell of gas. The explosion struck at around 9:30am and New York Fire Department said firefighters were on the scene two minutes later. "There was a major explosion that destroyed two buildings. The explosion was based on a gas leak," de Blasio said. - 'Tremendous' anxiety - It is the first deadly disaster of its kind to strike the city of eight million since the Democrat took office in January and will raise concerns about safety in less affluent neighborhoods. "There was no indication in time to save people. We know we have lost two people already," the mayor said. "There is a tremendous amount of anxiety, but suffice it to say that every effort is being expended to locate each and every one of these (missing) individuals," he added. De Blasio was careful to caution that some of those missing could simply be safe elsewhere and out of contact. A spokesman for New York Fire Department told AFP that firefighters were still putting out pockets of fire five and a half hours after first arriving on scene. Twenty-four people were injured he said, raising an earlier number of 22 given by police. A police spokesman said that two patients were in critical condition and five others were serious. Witnesses compared the scene of twisted metal, thick column of white smoke and dusty rubble to a war zone. Hundreds of police and more than 250 firefighters were on site with emergency trucks, as a dense column of smoke spewed into the sky over the Metro-North railway line, an AFP reporter said. The incident forced the indefinite suspension of train services in and out of Grand Central Station in midtown Manhattan. Jazzmen Arzuaga, 30, told AFP she was at work at a hospital when her wife rang to tell her what had happened. "She called me and told me 'Oh my God, you need to come home now, it's like World War II, people are dying, there was an explosion.' I just literally ran," she said. The couple live across the street from the blast. Arzuaga's wife Jay Virgo, 30, said she was lying in bed when the blast threw her to the floor. "I ran out of the building and I looked across the street and there were a couple of people lying on the floor. There was glass everywhere, huge pieces of glass. It just looked crazy," she said. Con Edison confirmed to AFP that a resident reported smelling gas inside the apartment building at 1652 Park Avenue but indicated the odor may have been coming from outside. "Our crews are checking our gas lines and working to isolate any leaks that they find and they're working closely with the FDNY to make the area safe," company spokesman Bob McGee said.