The four were killed yesterday after they entered the manhole in Qatar's capital Doha for cleaning, Gulf Times reported.
Sources said the four victims -Ishaq, 26, Faisal, 30, Muneer, 20 and Mohamed, whose age was not mentioned - were from Kerala.
Two of the four workers who went into the manhole fell unconscious and the others had followed them in a bid to bring them out, sources said.
They had reportedly taken the work on contract and were cleaning the manhole when they were trapped inside.