The worker went missing on Thursday afternoon in Nalgola of Ward No. 30, according to a bdnews24.com report.

Local resident Mojahidul Islam said several sanitation workers had been cleaning the drain since Thursday morning.

Speaking to bdnews24.com on Friday afternoon, he said, "A cleaning worker went down a manhole to clean it but went missing due to the toxic gas and hazardous conditions inside.

"About an hour after he entered the manhole, people began searching for him. Even by this afternoon, he had not been rescued."

Rashedur Rahman Russell, sanitation inspector for Ward No. 30 of the Dhaka South City Corporation, said, "We received the report that the worker had gone missing shortly after 1:00 pm [on Thursay], but he has still not been found.

"People at the scene said a cleaner entered the manhole carrying an adequate supply of oxygen and other equipment. Several government and private agencies are involved in the rescue operation.

“Efforts are being made to excavate the road from Nalgola to the embankment in an attempt to locate him."

Russell said the missing worker was employed by a contracting company but declined to identify the contractor.

Another local, Shafiqul Islam, said: "He went down into the manhole with an oxygen supply. About an hour later, the rope floated back up. It seems the rope may have become detached from his body."

Khaleda Yasmin, duty officer at the Fire Service control room, said: "Our Fire Service personnel have been carrying out rescue operations since [Thursday]. They are continuing their efforts."