Meanwhile the miner has announced an additional US$450 million spend to improve safety at the remaining structures at Córrego do Feijão and on recovery efforts.

Luiz Augusto Pessoa Nogueira told The Wall Street Journal Vale might have carried out an explosion at its mine less than a mile from the dam, hours before it collapsed.

"This is one of the hypotheses that we are investigating as being the trigger," he said.

However Vale has said this was not the case, saying it carried out two planned explosions after the dam collapse as a safety measure to eliminate leaving explosives in the ground.

About 300 people were killed or are still missing after the upstream tailings dam collapsed on January 25.

Vale announced yesterday it would spend a further BRL$1.8 billion (US$450 million) by 2023 on "several work fronts" at Brumadinho.

It said the funds, in addition to the $4.5 billion outlined in its first quarter results, would be used to ensure the geotechnical safety of the remaining structures at the Córrego do Feijão mine, the removal and proper disposal of tailings, as well as part of the environmental recovery, especially along the affected stretch of Paraopeba river.

In a video posted online, Vale detailed its measures to reduce the tailings flow into the Paraopeba River and said it had started to remove tree trunks and other materials so the fire service could continue its search for victims.

The iron ore price is above $115 per tonne for 62% fines according to MySteel, amid supply constraints as Vale's output has seen curtailments and Rio Tinto last week lowered guidance for its Pilbara iron ore shipments citing "operational challenges".