Three people were killed when a six-storey building collapsed outside New Delhi in India. More than 100 rescue workers were still searching for dozens of people feared trapped under the rubble of the building, which was still under construction when it gave way late Tuesday in Greater Noida just east of the capital. "We dont know exactly how many are trapped inside. We believe there are 12 people who may be trapped under the debris," regional chief fire officer Arun Kumar Singh told AFP. Sniffer dogs were also being brought in to assist with the search. The four-story building was 2 years old and only one family lived there, district magistrate B.N. Singh said. One security guard and some workers on the ground floor may have been inside at the time as well. The National Disaster Response Force, a federal rescue agency, was helping police in the search and rescue operations, Ravinder Singh, a NDRF official, said it would take several hours to clear the debris. Angry residents complained that the two buildings collapsed around 8:30 p.m. Tuesday (1500 GMT) but the police and fire services reached the site an hour and a half later. The rescue effort was slow to begin with, resident Praveen Srivastava told the New Delhi Television news channel. The building collapsed onto an adjacent newly constructed four-storey residential building, authorities said. Both are part of a residential complex in one of the many satellite towns dotted around Delhi growing fast to house the fast-expanding population of the 20-million-strong megacity and its environs. Parts of Greater Noida are notorious for rampant and unregulated construction, with many projects flouting building regulations and cutting costs and corners with substandard materials. Police arrested three people, including the landowner, over the latest accident. "We are questioning them to ascertain the kind of partnership they had with the builder... Strict action will be taken against those responsible," local officer Avnish Kumar told AFP. The cause of the building collapse was not immediately known. Building collapses are common across India, especially during the monsoon season from late June to September, although it was unclear whether this latest disaster was due to recent heavy rain in the Delhi region. At least 18 people died in May when a flyover collapsed in northern India, crushing vehicles and passengers under tonnes of concrete. Last year at least 30 people were killed in Mumbai after a 100-year-old house caved in. The worst collapse in recent decades killed at least 72 people in Mumbai in 2013.