By Agence France-Presse
The tailings dam, owned by Brazilian mining giant Vale, broke apart "very violently, very suddenly," sending a massive torrent of mud over the complex where hundreds of employees were working, Vale CEO Fabio Schvartsman told a news conference in Rio de Janeiro.
The deluge rumbled on to the nearby town of Brumadinho, located southwest of the city of Belo Horizonte, cutting a swath through vegetation, farmland and roads, and impeding access to the area.
The death toll was expected to rise, as rescue teams scoured through the disaster zone overnight into Saturday. Dozens of helicopters were being used.
Brazil's new government led by President Jair Bolsonaro reacted to its first big emergency since taking office early this month by launching disaster coordination between the defense, mining and environment ministries and authorities in the affected state of Minas Gerais.
Bolsonaro and his defense minister were to fly over the zone on Saturday. His environment minister raced to the area late Friday.
An AFP photographer viewing the zone from the air described tractors, houses and a bridge submerged in mud, and emergency crews using earth-moving machinery to search for survivors.
Television images earlier showed helicopters being used to rescue people stuck in mud.
Schvartsman called the dam break "a human tragedy, because we're talking about probably a large number of victims -- we don't know how many but we know it will be a high number."
Schvartsman, who had his two-year term renewed last month by Vale's board, said it was an "inactive dam" that was in the process of being decommissioned that burst apart.
Its contents -- tailings, or mining byproducts mixed with water -- cascaded into another dam, which overflowed, he said.
The liquid, brown mass barreled on towards Brumadinho, population 39,000, but did not deal it a direct hit.
The Minas Gerais government statement said 427 people had been working at the Vale mine at the time of the dam collapse, and 279 were recovered alive. The others were listed as missing.
"Where are our relatives?" wailed Raquel Cristina, one of several people demanding information in Belo Horizonte about their kin in the mud-hit area.
"My five-year-old nephew is asking me if his dad died. What do I tell him?" asked another, Olivia Rios.
Romeo Zema, the governor of Minas Gerais state, told reporters that, while all was being done to find survivors, "from now, the odds are minimal and it is most likely we will recover only bodies."
Vale shares plunge
Shares in Vale plummeted eight percent in New York trading Friday. The Sao Paulo stock market was closed for a holiday.
The disaster recalled trauma from a 2015 dam break in a different part of the same state of Minas Gerais, in Mariana, in which 19 people died.
That accident three years ago released millions of tons of toxic iron waste along hundreds of kilometers (miles), causing what is considered the country's worst environmental disaster. Vale was joint operator of that dam, along with the Anglo-Australian group BHP.
The Brazil office of Greenpeace, the environmental activist group, said Fridays dam break was "a sad consequence of the lessons not learned by the Brazilian government and the mining companies."
It said that the incidents "are not accidents but environmental crimes that must be investigated, punished and repaired."
Civil defense officials said people living in low-lying areas of Brumadinho had been evacuated after the collapse.
Vale issued a statement saying it had set up shelters for residents left homeless.
Brumadinho's municipality issued an alert on social media warning residents to move away from the Paraopeba river that the dam had been holding back.
The town is best known to tourists for Inhotim, an outdoor contemporary art museum, which was evacuated as a precaution. The venue receives 35,000 visitors a month.