Officials in Brazil say that blood and urine tests conducted on firefighters searching through muddy mine waste for missing people after a dam collapse show high levels of potentially toxic metals.

The Minas Gerais state government said in a statement on Wednesday that the tests showed "higher than recommended" levels of aluminum and copper, though no signs of "acute intoxication".

The mine collapse in January sent muddy tailings sweeping through the city of Brumadinho, killing at least 166 people, with 180 still listed as missing.

Officials didn't specify how many firefighters were tested and further details weren't immediately available.