Hundreds of people are feared dead after a dam operated by the mining company Vale collapsed in the Brazilian state of Minas Gerais, releasing a wave of red iron ore waste and causing the worst environmental catastrophe in the country’s recent history.

Some 34 bodies have already been found and more than 300 people remain missing, according to the company. The disaster comes only three years after a similar failure of the Fundão tailings dam near Mariana – co-owned by Vale – which killed 19 people.

Speaking after the latest disaster, the local fire chief Col Edgar Estevão said 100 people had been rescued from the sea of mud released by the dam. However, Vale later released a list of 412 employees and contractors whom it had still been unable to contact, and the state governor, Romeu Zema, said he did not expect many more survivors.

“We know now that the chances of having survivors are minimal and that we will probably rescue bodies,” he said.

Brazilian television showed images of survivors being winched to safety by a helicopter after the disaster at the Feijão mine near Brumadinho, less than two hours from the state capital, Belo Horizonte.

“I saw a gigantic cloud of dust and a wave of mud. It was one wave on top of another,” one contractor, Mayke Ferreira, told the Folha de S.Paulo newspaper. Ferreira said he had been sleeping in a nearby dormitory when he was woken by an enormous crash.

It is not yet clear what caused the tailings dam to burst. However, the Brazilian environmental agency Ibama has already slapped a 250m reais (£50m) fine on Vale for violations related to the tragedy. The company has caused pollution, made the area unfit for habitation and committed other regulatory violations, Ibama said. State prosecutors have also filed a request to freeze 5bn reais in Vale’s accounts to help fund recovery works.

Brazil’s new president, Jair Bolsonaro, visited Minas Gerais and flew over the disaster area. “We will do what is within our reach to attend the victims, minimise damages, investigate the facts, demand justice and prevent new tragedies like Mariana and Brumadinho,” he tweeted.

However, environmentalists have accused Bolsonaro of persistently attacking them for calling for tighter regulations at the mine and for failing to take action to tighten safety there.

“This tragedy was only a matter of time,” said Carlos Eduardo Pinto, a prosecutor who worked on the Mariana case. “Since the Fundão tailings dam, nothing has been done to increase control of this activity.”