"Hungary opened a criminal probe into the toxic sludge flood Wednesday while the European Union and environmental groups warned the disaster could spread down the Danube River and have long-term consequences for a half-dozen nations. Hundreds of people had to be evacuated after a river of red toxic waste, estimated to be one million cubic metres, poured through their towns Monday. The flood happened when a reservoir burst at an alumina refining plant in Ajka, about 160 kilometres southwest of Budapest. At least four people are dead, six are missing and more than 100 are injured. Emergency crews are trying to contain the damage as the sludge, which is still up to a metre thick in some locations, poured through several towns. Police spokeswoman Monika Benyi told The Associated Press the decision by National Police Chief Jozsef Hatala to take over the probe reflects the importance and the complexity of the sludge disaster. She said a criminal case had been opened into possible on-the-job carelessness. The huge reservoir was no longer leaking Wednesday and Interior Minister Sandor Pinter said guards have been posted at the site ready to give early warning in case of any new emergency. Henk Hirs, a Budapest-based journalist, told CBC News that emergency workers are trying to stop the sludge from getting to the Danube River. They're building temporary barriers, so they can slow down the sludge enough to scoop out as much as possible."