Four sanitation workers died of suffocation after inhaling toxic gases while cleaning the underground sewer of a Faridabad hospital on Wednesday afternoon, police said.

Rohit, his brother Ravi, Vishal and Ravi Goldar, residents of Sanjay Camp in Delhi's Dakshinpuri, had come to the QRG Hospital in Faridabad Sector 16 for sewer cleaning through an agency named Santosh Allied Service, they said.

"The four had entered the manhole without any safety equipment to clean. During this, they suffocated after inhaling poisonous gases and fell unconscious. When they cried for help, their colleagues and hospital staff reached the spot. All four were taken out and admitted to the hospital," ACP, Central, Mohinder Verma said.

"Soon after, the doctors declared all four dead. We are investigating the matter," he added.

The police have kept the bodies at the mortuary of Badshah Khan Hospital. Their families have been informed, the official said.

The police said the victims used to come to the hospital every month for work.

Distancing itself from the entire episode, the hospital management said the agency engaged for sewer cleaning services was responsible for the incident.

"Strictest action will be taken against those found responsible," Verma added.