The alarm went off at 5:30 am Sunday morning, warning of dangerously high water levels at a dam that is part of the Corrego do Feijao site, according to a statement by the Vale mining company.
A dam at the same mining site burst Friday, spewing millions of tons of sludge, sweeping away and burying buildings and people in its path.
Firefighters said they immediately began evacuating nearby communities.
Warnings blared through loudspeakers in Brumadinho, urging its 39,000 to "Find the highest point in the city" .
Vale's CEO Fabio Schvartsman and Minas Gerais Governor Romeu Zema earlier warned that the death toll from the Friday rupture could rise
"From now, the odds are minimal [to find more people alive] and it is most likely we will recover only bodies," Zema told reporters late Friday.
Among the more than 170 survivors rescued from the disaster, 23 were hospitalised with injuries.
Search and rescue operations, suspended overnight because of rain, resumed at 4 am (0600 GMT).
Dozens of helicopters were set to be deployed because the thick mud was treacherous for ground rescuers to venture into.
Brazilian President Jair Bolsonaro flew over the devastated zone on Saturday, later tweeting that it was "difficult to not be emotional before this scene."
The military said it deployed 1,000 soldiers, including sniffer dogs, to the disaster zone.
Separately, an Israeli team of 130 soldiers equipped with cellular location equipment, drones and naval sonars is set to reach the area Sunday to help search for survivors and bodies, an Israeli military spokesman said. The team is expected to stay for one week.
The disaster is the first big emergency faced by Bolsonaro and his government since he took office in early January, and may be one of the deadliest disasters in Brazil's history.