Stretches of the Danube River in Hungary are in danger following an accident at a chemical waste plant.

A reservoir at an alumina plant bust late on Monday evening, with some 600,000-700,000 cubic metres of toxic red sludge released.

A state of emergency has been declared by the Hungarian government in the county of Veszprem where the spill occurred, with at least seven villages and towns, including Devecser where the torrent was two metres deep, affected.

Four people have been killed and over 120 have been reported injured. A further six people are believed to be missing.

Some 7,000 people are believed to be directly affected by the disaster at the present time.

The towns of Gyor-Moson-Sopron and Vas, where the sludge appeared to be heading, have also been declared disaster zones.

The accident happened in the town of Ajka.

The sludge is believed to a mixture of water and mining waste containing heavy metals - is considered hazardous, according to Hungary’s National Directorate General for Disaster Management (NDGDM).

“People here speak of a mini-tsunami,” said NDGDM spokesman Gyorgy Bakos.

Some 7,000 people have been directly affected by the sludge

Danube

Flooding has been centred on the Torna River, with about 270 homes engulfed.

The sludge is presently spread over 16 square miles, according to the Environmental Ministry.

Officials are battling to limit the spread, with the Danube River in danger of being contaminated. Ministry officials warned the spill could have a lasting environmental impact on the popular tourist destination, causing long-term damage to ecosystems and killing fish and vegetation.

Hungarian prime minister, Viktor Orban, appealed for calm.

While acknowledging the scale of the disaster, he said the government had set up a special team of experts to analyze the accident. Human error was cited as the most likely cause.

He also stressed that there was no threat of radiation in the area affected by sludge.

Red sludge is a by-product of the refining of bauxite into alumina, the basic material for manufacturing aluminum, according to the Aluminum Association.

The sludge, a waste product, contains heavy metals and is toxic if ingested, scientists say.

However, the owners of the reservoir issued a statement earlier today rejecting claims the sludge was toxic according to European Union standards.