RIO DE JANEIRO, Jan. 29 (Xinhua) -- Brazilian authorities on Tuesday arrested five people in connection with the iron-ore waste dam collapse last week, which killed scores and causing an environmental catastrophe.

Police arrested three employees of mining giant Vale, which owns the mine in Brumadinho in the southeast state of Minas Gerais, and two subcontracted engineers.

The employees "were directly involved in the licensing of the dam that collapsed," and the engineers "had declared the dam was stable," state news agency Agencia Brasil said.

While arresting the suspects, who will be detained for a period of 30 days, police officers also took away loads of documents as evidence.

"It is hard to believe that a dam with this size -- run by one of the world's biggest mining firms -- can burst unexpectedly, without any sign of vulnerability," said Perla Saliba Brito, the federal judge that ordered the arrests.

The dam was reportedly equipped with sensors capable of detecting signs of structural weakening.

The incident marks the second tailing dam collapse in just three years at a Vale-owned mining operation in Brazil, flooding communities and fields with toxic sludge.

In November 2015, a tailings dam partly-owned by Vale ruptured in Mariana, also in Minas Gerais, destroying an entire community and killing 19 people. It was considered Brazil's worst environmental disaster.