A rescue worker carries an injured girl at the site of a building collapse in New Delhi November 16, 2010. A residential building collapsed in Lalita Park in New Delhi's Laxmi Nagar area on Monday evening. [Photo/Agencies]

NEW DELHI- Rescuers raced Tuesday to pull survivors from the debris of a four-story apartment building that collapsed into a mountain of concrete slabs in a poor neighborhood of New Delhi, killing at least 61 people and injuring scores of others.

The 15-year-old building housing about 200 people _ mostly migrant workers and their families _ collapsed Monday evening in New Delhi's congested Lalita Park area, and emergency efforts initially were hampered because vehicles had difficulty navigating the neighborhood's narrow alleyways.

About 30 people were believed still trapped under the rubble, said New Delhi's top elected official, Sheila Dikshit.

The death toll reached 61 as police and rescuers pulled bodies from the site and 78 people were injured, city police official Mohammed Akhlaq said.

An adjacent building, also in danger of collapse, was evacuated, Akhlaq said.

The cause of the collapse was not immediately clear, but one official said the building may have been weakened by water damage following monsoon rains. Police said they were looking for the building's owner.

Local residents who were first to arrive at the accident site used bare hands to dig into the piles of concrete, bricks and mortar, until they were joined by police and firefighters, who used gas cutters to cut through the iron rods jutting from the wreckage. Police brought in sniffer dogs to locate people trapped under the debris.

Residents helped carry the injured to vehicles and to transport them to nearby hospitals, as hundreds of people crowded around or peered down from rooftops of nearby buildings.

Dikshit said there would be an inquiry into the cause of the collapse.

"The scale of the tragedy is unprecedented. I don't think such a tragedy has taken place in Delhi in the recent past," Dikshit said.

New Delhi's finance minister, A.K. Walia, told Press Trust of India that this year's unusually heavy monsoon rains could have weakened the building's foundation. He said floodwaters of the Yamuna River had inundated the area two months ago.

Residents said rainwater had accumulated in the basement of the building, but it was not immediately clear if it had been pumped out.

Police said they were searching for the owner of the building, identified as Amrit Singh, a building material trader.

Poor construction material and inadequate foundations often are blamed for building collapses in India. In New Delhi, where land is at a premium, unscrupulous builders often break building laws to add additional floors to existing structures.