The order to evacuate on Monday afternoon ripped through Nysa, a small Polish city, drenched after days of heavy rains. Some people helped older neighbors into cars as they headed for higher ground. Others raced to the roadside embankment to try to prevent the surging river from overflowing.

Together, thousands worked through the rainy night, passing sandbag after sandbag along a lengthy human chain — including the city’s professional men’s volleyball team. By morning, the danger seemed to have passed and disaster had been averted, thanks in no small part to the heroic efforts of its inhabitants.

“Everything indicates that Nysa is saved,” Kordian Kolbiarz, the mayor, wrote in a euphoric Facebook post on Tuesday. “Yesterday’s ‘chain’ on the top of the embankment did its job!”

Nysa, near the Czech border, is just one community in Central Europe that has stared down the devastation of Storm Boris, which has been blamed for at least 20 deaths in recent days. Towns have flooded, bridges have been destroyed and dams have been breached. Thousands of people have been forced from their homes.

The rains have abated in parts of Poland, where at least seven people died during the storm, the Polish Press Agency reported on Tuesday. But parts of Italy were bracing for heavy rains. Some public services and transit options remained interrupted in Budapest, the Hungarian capital on the Danube, which is swollen with rainwater.

In Nysa, the 42,000 residents had been preparing for days, despite reassurances from the authorities. Many remembered the 1997 floods that killed more than 100 people in the region and displaced thousands of others.