Police in southern India have detained two construction company directors as rescuers continued searching for missing workers in one of two weekend building collapses that killed at least 22 people.

The 12-storey building under construction in Tamil Nadu state collapsed late on Saturday, killing four workers on the spot and another seven succumbed to injuries later in a hospital, said police officer George Fernandes.

Authorities said 31 construction workers had been pulled out of the rubble so far and the search was continuing for more than 100 people thought to be trapped under the rubble of the tower, that collapsed while it was still being built.

Fourteen workers remained hospitalised, while six others were discharged, Fernandes said.

Police officer Kanan said two directors of the construction company, Prime Sristi, have been detained for questioning as authorities began investigating the collapse. The officer uses one name.

Balaguru, one of the builders, said the structure collapsed possibly due to the impact of lightning.

"Usually, once the construction gets over we install the equipment to prevent the building from a thunder strike. It was nearing completion", the Press Trust of India news agency quoted Balaguru, who uses one name, as saying.

Builder mafia 

Nearly 300 police and fire service workers worked overnight, looking for survivors in the debris. "Removing debris is a major challenge. It may take two to three days to clear the rubble", said S P Selvam, who is heading the rescue operation.

Earlier on Saturday, eleven people including five children were killed in New Delhi after a 50-year-old apartment block with 14 occupants collapsed, authorities said.

Numerous building accidents in India's largest cities have killed about 100 people in the past year, according to local media reports. More than 50 people were killed when an apartment block collapsed in Mumbai last September.

Delhi's Deputy Commissioner of Police Madhur Verma told reporters an investigation into the cause of Saturday's building collapse had been launched.

Former Delhi chief minister Arvind Kejriwal called the incident a "nexus between the builder mafia and the municipal corporation". The corporation did not answer phone calls requesting comment.

Source: Al Jazeera and agencies