Between 100 and 150 of those missing were in the dam's complex, firefighters said.
"I'm anxious, I want news," 28-year-old Helton Pereira told BBC News Brasil as he waited outside a hospital in nearby Belo Horizonte - his 28-year-old wife and 35-year-old sister worked at the dam's cafeteria and were both missing.
The search is being carried out by 100 firefighters with 100 more expected to join them on Saturday.
"From now, the odds are minimal and it's most likely we'll recover only bodies," Gov Zema said.
Built in 1976, the dam was one of several in the area and it was used to hold residue from the mine.It had capacity for 12m cubic metres and had been an inactive site for three years, Vale said. It is not yet known how much waste was released.
What has the reaction been?
President Jair Bolsonaro called it a "serious tragedy" and said he would fly to the affected area on Saturday.
"Our main concern at this moment is attending to potential victims of this grave tragedy," he said on Twitter.
The environment, mining and regional development ministers were also travelling to the region.
Vale chief executive Fabio Schvartsman called it a "human tragedy" and said a German company, hired to assess the dam, indicated in the most recent report last September that it was stable.
The firm said it was monitoring all its other dams.
A report by Folha de S.Paulo newspaper said the risk of collapse of the dam had been mentioned in a "tense meeting" that approved its licence last month (in Portuguese).
The environmental activist group Greenpeace said the dam break was "a sad consequence of the lessons not learned by the Brazilian government and the mining companies."
It said the incidents "are not accidents but environmental crimes that must be investigated, punished and repaired."
What happened in 2015?
On 5 November 2015, a dam - also owned by Vale, along with BHP Billiton - burst at a Samarco mine in Mariana.
More than 60m cubic metres - enough to fill 20,000 Olympic swimming pools - spilled over into the surrounding area.
After a lengthy court case, BHP Billiton and Vale reached a settlement worth at least 6.8bn reais ($1.8bn) with the Brazilian government.
