A building being constructed illegally in a suburb of India's financial capital Mumbai has collapsed into a mound of steel and concrete, killing at least 41 people and injuring more than 50 others, authorities say.
Rescue workers with sledgehammers, petrol-powered saws and hydraulic jacks were struggling to break through the tower of rubble in their search for possible survivors. Six bulldozers were brought to the scene.
"There may be (a) possibility people have been trapped inside right now," local police commissioner KP Raghuvanshi said.
More than 20 people remained missing and three floors of the building remained to be searched, said RS Rajesh, an official with the National Disaster Response Force.
"All the three floors are sandwiched ... so it's is very difficult for us," he said, adding that rescuers were continuing to pull survivors from the wreckage.
The dead included at least 11 children, police said.
At least four floors of the planned eight-storey building had been completed and were occupied. Workers had finished three more floors and were adding the eighth when it collapsed, police Inspector Digamber Jangale said. Some of the dead were construction workers staying in the building as they worked on it.
The building did not have the necessary clearances from local authorities, he said.
It was not immediately clear what caused the structure to collapse, but Mr Raghuvanshi said the building structure was weak. Police were searching for the builders to arrest them.
"The inquiry is ongoing. We are all busy with the rescue operation; our priority now is to rescue as many as possible," he said.
Police with rescue dogs were searching the building, which appeared to have buckled and collapsed upon itself. Rescuers and nearby residents stood on the remains of the roof trying to get to people trapped inside. Residents carried the injured to ambulances and one man carried a small child caked white with dust from the wreckage.
Mr Raghuvanshi said rescue workers had saved 15 people from the wreckage.
Building collapses are common in India as builders try to cut corners by using poor quality materials, and multi-storied structures are built with inadequate supervision. The massive demand for housing around India's cities and pervasive corruption allow builders to add unauthorised floors or build entirely illegal buildings.
Officials said the neighbourhood where the building collapsed was part of a belt of illegal structures that had sprung up in the area in recent years.
"There are lot of people involved (in illegal construction) - builders, government machinery, police, municipal corporation - everybody is involved in this process," GS Khairnar, a former top Mumbai official, told CNN-IBN television.
A local resident, who did not give his name, said the site was meant to hold a smaller structure and accused officials of turning a blind eye to the problem.
"They made an eight-storey building of what was supposed to be a four-storey building. People from the municipality used to visit the building but the builder still continued to add floors," he said.
In one of the worst recent collapses, nearly 70 people were killed in November 2010 when an apartment building in a congested New Delhi neighbourhood crumpled. That building was two floors higher than legally allowed and its foundation appeared to have been weakened by water damage.