No one was injured till last reports were received, a senior officer of Kolkata Police said.
A portion of the almost century-old building at 10 Mirror Street under Taltala police station limits collapsed at around 12.45 pm, the police officer said.
"Luckily nobody was hurt as some inmates managed to rush outside," he said. "We fear that a few are still stuck inside," the officer said.
Two fire engines and a huge team from the fire department along with personnel from Disaster Management units and police personnel from the local police station were conducting the search, the officer said.