BENTO RODRIGUES, Brazil (REUTERS) - Rescuers abandoned a search for seven-year-old Tiago Damasceno in the muddy aftermath of a Brazilian dam collapse on Tuesday, as hope for survivors diminishes five days after the disaster.

Rescuers had waded some 300m through waist-deep mud, to a house where the boy had been with his grandmother when the disaster happened. She was knocked unconscious during the flood but was found alive several metres away.

The child's father, Albertino, an employee of Samarco, the Vale-BHP Billiton joint venture that owned the mine where the two dams burst, accompanied the search.

As the effort was called off, he returned heavy with mud, too distraught to speak to reporters.

"We went back with sniffer dogs to be sure we wouldn't find anything, but unfortunately, we had to end the search," Major Rubem da Cruz of the local fire department told Reuters.

Santos is one of 22 people still missing after one of the worst mining disasters in Brazil's history. Four deaths have been confirmed.

One person thought to have been missing was found on Tuesday staying with family in a neighbouring town, but the chance of finding those swept away alive is fading fast.

No cause has been identified for the dams' failure, which left about 750 people homeless.

The destruction reached as far as 100km from the burst dams, with dozens of houses now little more than bare walls.

Firefighters have managed to open one street in the worst affected village of Bento Rodrigues, but for many there is no home to go back to.