Image copyright Reuters Image caption In some areas the mud is up to 15m deep

Eight employees of the Brazilian mining giant Vale have been arrested as part of the criminal investigation into the breaking of a dam last month.

The breaking of the Feijao dam, which was used to collect mining waste, killed at least 166 people in the town of Brumadinho. 147 are still missing.

Search warrants have been issued for four people from German consultancy firm Tüv Süd.

The arrests were made in São Paulo, Rio de Janeiro and Belo Horizonte.

Two of the arrested are Vale executives. They will all be questioned by investigators in Belo Horizonte.

Tüv Süd carried out an audit in September last year which found the dam met legal requirements.

But earlier this week, an internal report seen by the Reuters news agency said the Brazilian mining company knew the dam was at risk as it was told the site breached guidelines months before it collapsed.

Vale, which is the world's top iron ore miner, said the report was misleading as there was no evidence of imminent risk.

The collapse of the dam was the second major mining disaster in the region since 2015, when a nearby dam co-owned by Vale collapsed.

Analysis:

Daniel Gallas, South America business correspondent

In the aftermath of the 2015 Vale disaster, Brazilian authorities were severely criticised for being too slow and complacent. No one has yet been sentenced for that accident.

This time judges, investigators and politicians are showing a different attitude. This month 17 employees have already been detained for questioning. Court orders are suspending some of Vale's most profitable operations and freezing the company's assets.

Vale's answer to both accidents is drawing the ire of the Brazilian public as was clear from a disastrous appearance by Vale chief executive, Fabio Schvartsman, at a Congressional hearing on Thursday.

The executive was evasive when questioned about why the company had not yet paid many fines regarding the 2015 disaster.

At one point Mr Schvartsman said Vale "is a Brazilian jewel" and "cannot be condemned for an accident that happened in one of its dams - even though it was such a big tragedy", drawing angry replies from lawmakers.

The company's failure to respond adequately is increasing the charge from authorities. Politicians will set up a Congress inquiry about Vale in the coming days. Stricter mining legislations are also under consideration.

Read more from Daniel: From the pride of Brazil to most hated company

It is still not known what caused the collapse at Brumadinho, but experts believe liquefaction was to blame.

Liquefaction is a process whereby a solid material such as sand loses strength and behaves more like a liquid.

The company has lost a quarter of its market value - or nearly $19bn - since the disaster on 25 January.