At least 12 people, including an infant, were killed in a fire Thursday night in an apartment building in the borough of the Bronx, officials said. The main cause is under investigation. Mayor Bill de Blasio called it the "worst fire tragedy in this city in at least a quarter century." "Four people were in hospital in critical condition fighting for their lives," he added. The fire took place around 7 p.m. on the first floor of a brick building and swiftly spread upstairs, according to statements by city Fire Commissioner Daniel Nigro. The blaze erupted in the Belmont section of the Bronx, a primarily residential, close-knit neighborhood known as the “Little Italy” of the borough, adjacent to the Bronx Zoo and Fordham University, Reuters reported. Four people were critically injured and others were hurt, Blasio said, adding the possibility that "we may lose others as well." The victims died on various floors of the apartment building. "People died on various floors, they range in ages from one to over 50," Nigro stated. "This tragedy is, without question, historic in its magnitude. Our hearts go out to every family who lost a loved one here and everyone fighting for their lives," he added. In March 2007, 10 people were killed in another fire in the Bronx that tore through a home to two immigrant families, itself the worst fire in the city since 1990, AFP reported.