The mayor of the Polish-Czech border town of Český Těšín ordered the evacuation overnight of several thousand residents from the city centre as the Olsa, a tributary of the Oder river, threatened to burst its banks. In the city of Opava, on the river of the same name, thousands of people left their homes earlier due to acute flooding danger. Among the districts affected was the city’s largest high-rise housing complex. People were also brought to safety in Krnov and other towns. In the Hrubý Jeseník, the 2,000-inhabitant community of Česká Ves was cut off from the outside world by the high wat…