Ten children are among at least 18 people reported missing after a sewage-polluted river swollen by heavy rains swept away precarious homes in the Guatemalan capital, authorities said Monday.

A tributary of the Las Vacas river washed away six homes in an informal settlement erected under a bridge in the centre of Guatemala City, Rodolfo Garcia, spokesman for the Conred disaster relief agency, told reporters.

Hundreds of indigent people had erected homes consisting mainly of zinc sheets on the banks of the tributary despite a municipal ban due to it containing residential wastewater from the capital's sewage system.

Water-bearing stones, soil and human waste gushed through the settlement following heavy rains on Sunday, leaving just debris in its wake, an AFP reporter observed.

Conred said a search and rescue operation was underway for at least 18 people who were swept away and are missing and the needs of the affected community were being assessed.

Resident Esau Gonzalez, a 42-year-old casual worker, recalled how "the river... took homes, neighbours' belongings. Neighbours disappeared."

Gonzalez told AFP the people of the community had nowhere else to go.

"The river took entire families," added Marvin Cabrera, 36, a motorcycle food delivery agent.

"We knew the risk, (but) we are here out of necessity," he added.

Tens of thousands of Guatemala's 17.7 million inhabitants depend on precarious housing in often hazardous environments in a country with a 59-percent poverty rate.

The country has a housing deficit of about two million units, according to the Guatemalan Chamber of Construction and the ANACOVI Builders' Association.