The construction workers were believed to be Indian nationals, New Delhi’s embassy said in a statement on Twitter.
“Rescue teams recovered the bodies of six Asian workers that were buried in a water project” in the coastal city of Seeb, about 30 kilometres (18 miles) northwest of the capital Muscat, the Public Authority for Civil Defense and Ambulance said.
“The workers were trapped in rainwater and mud while laying downpipes… underground in a site that was 295 metres (968 feet) long and 14 metres (46 feet) deep.”
It took rescue workers about 12 hours to recover the bodies after pumping the water out, the authority say.
The Indian embassy wrote: “We are deeply saddened to learn about the incident involving the deaths of six workers, who are believed to be Indian nationals”.
PACDA urged companies in charge of construction projects to abide by safety regulations to protect workers.
The General Federation of Oman Trade Unions called for an investigation to “clarify the circumstances behind the incident and for the necessary legal procedures” to follow.