More than 100 Indian rescue workers were using steel cutters and drills on Wednesday to try and free those still feared trapped under the rubble of a collapsed six-storey building outside Delhi.
Five bodies have been pulled out of the wreckage since the building gave way late Tuesday, according to rescue officials.
A rescue official told AFP it was not yet possible to determine how many people were still trapped underneath tonnes of concrete and metal debris.
Eyewitnesses and neighbours said one of those still missing was a one-year-old child from one of two families thought to be under the debris and who had moved in only days before.
"My friend was living here with his family since last Saturday. I spoke to them last night but have not had any contact with them since 9:00 pm," local resident Sandesh Kumar told Indian television news channel NDTV.
"I am just hoping they are alright," he said.
Sniffer dogs were also brought in to assist with the search, which officers said would continue through the night.
Authorities said the structure, which was still under construction, collapsed onto an adjacent newly constructed four-storey residential building.
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.
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.
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.
