Hungary declared a state of emergency on Tuesday after a toxic mud spill killed four people and injured more than one hundred and twenty others in what officials described as Hungary's worst-ever chemical accident. Officials fear, the death toll could rise after the walls of a reservoir of residue at an aluminium plant in Ajka, 165 kilometres west of Budapest, broke on Monday. Up to 40 square kilometres of land were affected and there were fears that some of the sludge had already found its way into the Marcal river and could therefore potentially pollute the connecting Raba and Danube rivers. The red mud is a toxic residue left over from Aluminium production and contains harmful substances such as lead as well as highly corrosive elements. The owners of the reservoir, the Hungarian Aluminium Production and Trade Company (MAL), said it had started repair work on the damaged tanks to prevent further spills.