A half-finished building that was being constructed illegally in a suburb of India's financial capital has collapsed, killing 35 people and injuring more than 50 others, police said Friday.

The building in the Mumbai suburb of Thane caved in at 6:08 p.m. Thursday, police said. Rescue workers with sledgehammers, gasoline-powered saws and hydraulic jacks were struggling to break through the rubble in their search for possible survivors. Six bulldozers had been brought to the scene.

"There may be (a) possibility people have been trapped inside right now," the local police commissioner K.P. Raghuvanshi said Friday.

More than 20 people remained missing and three floors of the building remained to be searched, said R. S. Rajesh, an official with the National Disaster Response Force who was at the scene.

`'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.

Among the dead, were at least 11 children, police said.

At least four floors of the building had been completed and were occupied. Workers had finished three more floors and were adding an eighth floor when it collapsed, police inspector Digamber Jangale said. Some of the dead were construction workers staying in the building as they worked on it, Jangale said.

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 Raghuvanshi said the building structure was weak. Police were searching for the builders to arrest them, he said.

`'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 Friday, which appeared to have buckled and collapsed upon itself. Rescuers and nearby residents stood on the remains of the roof trying to get to the people trapped inside. Residents carried the injured into ambulances and one man carried a small child caked white with dust from the wreckage.

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.

A local resident, who did not give his name, said the site was only meant to hold a smaller structure and said officials turned a blind eye to the problem.

"They made an 8 story building of what was supposed to be a 4 story building. People from the municipality used to visit the building but the builder still continued to add floors," he said.