BELGRADE, Serbia (AP) — Authorities in Western Balkan countries warned citizens Friday to be cautious, drink water and avoid sunshine during an early heat wave that sent temperatures soaring to up to 40 degrees Celsius (104 degrees Fahrenheit.)

“Don’t stay in the sun between 11 a.m. and 5 p.m.,” warned Serbia’s Public Health Institute in its instructions to citizens. “If you must go out, please take a bottle of water along.”

Meteorologists say the heat in the region this week came from Africa, carrying sand particles that created a cloud-like layer dimming the skyline.

The sweltering heat was the worst in big cities, where concrete sizzled even in the evening, and where nights offered no respite as temperatures remained above 20 degrees Celsius (68 degrees Fahrenheit.)

While hot summers are normal in the Balkans, temperatures don't reach such heights in mid-June, prompting weather alerts and warnings.

Earlier this week, authorities in North Macedonia imposed emergency measures through to Sunday, after which the heat is expected to relent.

Belgrade resident Milos Jeftovic said he is following the instructions and taking every opportunity to stay near the Serbian capital's two rivers. Authorities, he said, should have reduced working hours and parked water tankers in the city streets.

“Personally, I don't have a problem ... but this is not OK, temperatures are above acceptable (levels),” said Jeftovic.

Weather warnings were also issued in neighboring Croatia, a tourism hotspot, where the heat wave is set to peak on Friday ahead of an expected change of weather on the weekend that could trigger storms.

Montenegrin state RTCG television said that though the citizens of the country's capital of Podgorica are used to very high temperatures, some complained they started too early. One man told the TV station, “I really don't know what we are going to do.”

Experts say that extreme weather conditions are also triggered by climate change.