BERLIN (AP) — Authorities in Germany warned of heavy rainfall in the south Friday and put air rescue services on high alert, after severe storms killed at least 13 people elsewhere in Europe a day earlier.

Two girls, ages 4 and 8, were killed when sudden strong winds toppled trees late Thursday at a lake in the Lavant Valley of southern Austria. Officials said 13 people were injured, two of them seriously. Many of the victims were vacationers visiting the tourist region.

Austrian President Alexander Van Der Bellen called the children’s deaths “an unfathomable tragedy.” The mayor of the nearby town of Wolfsberg, Hannes Primus, said the area looked “like a battlefield.”

In Lower Austria, three women were killed when lightning struck a tree near the central town of Gaming, causing it to fall over.

Fierce storms also killed at least eight people in France and Italy on Thursday.

Germany’s national weather service DWD warned of “extremely abundant, prolonged rain” along the edge of the Alps could drop as much as 140 liters of water per square meter (5.5 inches) over a 48-hour period that could cause flooding.

The Bavarian Red Cross said it was raising the alarm level for its air rescue specialists, putting helicopter crews on heightened alert.