A week after the disaster, footage has emerged of the exact moment the dam burst, causing a mudslide that engulfed buildings and vehicles in the nearby city of Brumadinho.
Chewbacca, a rescue dog, searches for victims at Corrego do Feijao, where a dam collapsed at an iron-ore mine belonging to Vale near the town of Brumadinho.
Dams holding mining waste, known as tailings, sometimes collapse for this reason.
The death toll from a dam collapse last week at a mine in southeast Brazil has risen to 121 dead and 226 missing, officials said Saturday.
Employees of the mining complex were eating lunch when the dam gave way.
The wave of mud is now moving toward the Sao Francisco at about 1km/h but officials hope the Retiro Baixo hydroelectric dam and plant complex about 300km from Brumadinho will prevent the mud from contaminating it. The catastrophic failure of a dam jointly owned by the mining company flooded the river below with toxic iron waste, killing 19 people and displacing hundreds more.
Hildebrando Neto, deputy minister for environmental regulations in the state of Minas Gerais where the collapsed dam is based, told Reuters late on Thursday that all evidence suggests that the burst was caused by liquefaction, a process whereby a solid material such as sand loses strength and stiffness and behaves more like a liquid.
"It is totally devastated; it looks like there has been a war", said 23-year-old Edvan Cristi, who lost friends who worked at the mine. Authorities have frozen over United States dollars 3 billion in company assets for it to pay damages and compensation.