An under-construction school building collapsed in Koranthangal area of Vellore district, trapping labourers at work. Authorities have launched a rescue operation and pulled out seven persons so far. "We are seeing if there are more people. Seven workmen have been rescued so far," a senior police official told, adding, the rescued persons were rushed to a hospital. The roof of the building at Koranthangal collapsed suddenly and the reason for it is not known immediately, he said. Fire and rescue services and police personnel are engaged in rescue work. Excavators have been deployed to clear the rubble.