New Delhi, Jul 15 (IANS) : Four persons died in the national capital after inhaling poisonous gases as they entered a water harvesting tank to clean it on Saturday, police said.

While police said it was a water harvesting tank, family members of the deceased said the owner of the building had waste material pipes linked to the tank, but did not tell them about it, which led to their death.

Deputy Commissioner of Police Ishwar Singh said police got a call around 10.45 a.m on Saturday that five persons had fallen into a water harvesting tank in a building in Ghitorni area of south Delhi.

The police officer said that they were taken to different city hospitals where four of them were pronounced dead, while the fifth person survived.

He identified the deceased as Swarn Singh, 45, Deepu, 28, Anil, 23, and Billu, 32 -- all residents of Ambedkar Colony in Mehrauli area of the city.

Family members of the deceased said that the underground tank was about 10-feet-deep and 12-feet-wide and had a three-feet-wide opening.

Swarn Singh's son Satpal Singh said the owner of the building told them that they had to clean the harvesting tank but did not tell them that it was connected with the waste carrying pipes.

"They had connected waste pipes from kitchen and toilet to the tank, and the people who went to clean it had no idea about it," he told IANS.

Satpal's twin brother Jaspal Singh, who had gone into the tank to save his father, was the only survivor.

"The tank had all sorts of waste and that killed my son. We've lodged a police complaint," Billu's father, Satnam Singh, 60, said.

Police said they had registered an FIR in the case but were yet to ascertain whether pipes carrying waste materials were connected with the water harvesting tank.

"It has come to our knowledge that waste material pipes were connected with the tank, but it has not been confirmed. Also, we are yet to make any arrests in the case," a senior police officer privy to the investigation said.