Twenty people, including eight children, were killed and 21 others were injured when a portion of a four-storey building in south Mumbai collapsed in the wee hours on Monday, officials said.

The dead included eight children, same number of women and four men, they said adding, the injured were admitted to the government-run J J Hospital.

A portion of the building Dutt Niwas collapsed at around 5:15 am, Deputy Commissioner of Police (Zone II) R E Pawar said.

"Rescue efforts were hampered by narrow lanes leading to the site as well as rains," he said adding the bodies were being extricated from the rubble till evening.

Many residents on the higher floors of the building survived while those on the lower floors who were not so fortunate were trapped under the rubble, Pawar said.

The tenants of the building which was 70 to 75 years old had been asked to evict their homes in 2007 due to its dilapidated condition, a spokesperson for the Maharashtra Housing and Area Development Authority said.

"The notice had been issued last year and the tenants had been asked to evict their homes. The tenants were not co-operating in conducting the repairs suggested and negotiations were on," the spokesperson added.

One of the residents of the area said they had heard a loud sound and emerged out of their homes to find that the portion of the building had collapsed.

"Two of my relatives, Pramod and Priti Chaurasiya, were recently married and were living in one of the rooms. Both are now dead," Sunita Chaurasiya, who was waiting outside the J J Hospital said. She lost six relatives in the incident.

Six members of the Chaurasiya family, Raju (22), Renu (25), Hemant (3), Shivam (6), Pramod (26) and Priti (20) were killed in the incident.

The other deceased were identified by the hospital authorities included Shyam Sunder (31), Pradipkumar Das (26), Shobha Chavan (35), Kavita  Chavan (26), Samir Chavan (3), Ambika Chavan (3), Priyanka Salunkhe (2), Shweta Salunkhe (7), Sarika [Images] Salunkhe (26), Payal Salunkhe (10) and Kalabai Salunkhe (55).

A body of a 30-year-old woman has not been identified so far, hospital authorities said.

Chief Minister Vilasrao Deshmukh visited the accident site in the morning and announced a compensation of Rs 1 lakh each to the families of the deceased and Rs 50,000 to the injured.