Authorities in Serbia and Croatia warned citizens to stay out of the sun and drink a lot of water Monday during a heat wave that has hit the Balkans this week.

The spate of extreme weather sent the temperatures soaring toward 40 degrees Celsius (104 Fahrenheit) and brought warm winds to some areas.

A large fire erupted on the outskirts of the Montenegrin capital of Podgorica, threatening suburban homes. Firefighters used water-dropping planes to battle the blaze.

In Belgrade, the Serbian capital, authorities placed water tanks in the city center. Workers at the Belgrade Zoo have been cooling birds with water and feeding fresh vegetables and fruit to other animals.

Zoo employee Jozef Ezvedj says most animals spend hot days quietly in the shade.

Beaches along the Adriatic coast were full of tourists despite the heat warnings. Several small fires also have been reported.