By Aleksandar Vasovic

CACAK, Serbia (Reuters) - Police in Serbia ordered the evacuation of several thousand villagers in the southwest of the country on Saturday as over-stretched emergency services, backed by a Russian plane, battled wildfires scorching the western Balkans.

Near the Serbian town of Cacak, fires raged through hillsides and cornfields dried to a crisp by drought, a Reuters correspondent reported. Several houses were ablaze.

Police said they had ordered the villages of Miokovci and Gornja Gorevnica, near Cacak, to be evacuated.

"The situation ... is extremely serious and both settlements are endangered," said Predrag Maric, head of the Serbian Interior Ministry's Emergencies Department. "We are relocating manpower from throughout Serbia as well as helicopters to fight this."

The western Balkans is in the grips of a heatwave that has seen temperatures top 40 degrees Celsius (104 degrees Fahrenheit), triggering hundreds of wildfires.

Serbia and neighboring Bosnia appear to be worst hit.

A Russian Beriev Be-200 fire-fighting aircraft, with a capacity of 12 tonnes, arrived in Serbia on Saturday to provide extra air support. A Russian helicopter has been in action for days.

Police said the worst fires were in the Cacak region and the western Tara National Park, a popular tourist spot.

Fires also burned in the eastern Bosnian region of Bratunac, where helicopters of the European Union's Bosnian peacekeeping force were deployed on Friday to help douse the flames.

(Writing by Matt Robinson; Editing by Alison Williams)