The number of those affected by the landslide could reach more than 2,000 as the current continues to advance towards neighboring towns. Officials have not said what caused the accident.
At least 17 people have died and more than 50 have been injured on Thursday after two waste dams ruptured at a mining complex, causing a landslide in Bento Rodrigues, a town in the Brazilian state of Minas Gerais.
Images from Globo TV showed the area awash in a sea of clay-red mud that tossed cars on their sides and blanketed buildings. The inhabitants in the valley hit by the landslide were evacuated.
State fire department officials said Friday that the missing toll could rise, and that about 500 of the nearly 600 people thought to live in the area had been accounted for so far.
"In reality there are a lot more, but we can't confirm any more than that. We don't even know that we'll find everybody," said firefighter Adão Severino Junio.
According to the fire department, rescue work has been difficult by the still-wet mud, which could behave like quicksand.
Still waiting on an official response
The rupture at the mining complex owned by the venture Samarco unleashed a mix of water and ore mining residue on a small village 7 kilometers (4.5 miles) downhill and raised fears of an expensive cleanup.
Authorities on Thursday said one dam at the Samarco iron ore mining operation had burst roughly 20 kilometers from the city of Mariana, which is 300 kilometers north of Rio de Janeiro.
But in a video posted later on Samarco's Facebook page, company President Ricardo Vescovi said two dams at the facility had failed.
"Our focus in this critical moment is to preserve the integrity of people and of the environment," Vescovi said in the video.
"We are deeply sorry and we are very moved by what happened, but we are also in full action to stop the damage caused by this tragic accident."
Too early to know
The firm said it was too early to know the reasons for the disaster or the extent of carnage.
The dams had valid licenses from environmental authorities, who last inspected them in July, according to Samarco.
The dams are composed principally of sand and inert tailings, a mining waste product of metal filings.
Tailings dams sometimes hold chemicals, adding to fears of potential contamination of the nearby Gualaxo do Norte river, but Samarco said there were no chemical elements presenting health risks.
Samarco is jointly owned by the Brazilian mining company Vale and Australia's BHP Billiton.
hf/rc (Lusa, Reuters, dpa)