Smoke from fires raging across Russia's vast forest wilderness has engulfed the far eastern city of Yakutsk, forcing citizens to close doors and windows despite the summer heat, and to wear breathing masks.

Emergencies have been declared in seven regions of Russia due to the fires, according to Russia's forestry service, which collates satellite data on the fires. Around 4,000 people are involved in fighting them.

The worst-hit areas are the vast Yakutia region, also called the Sakha Republic, followed by the Khabarovsk, Amur and Krasnoyarsk regions,

Andrei Konoplyov, Yakutia's deputy ecology and forestry minister, told Reuters Television on Wednesday there were currently 111 forest fires in his region alone, covering 1,800 sq km (695 sq miles).

Yakutsk resident Lyubov Kolesova said she would usually be opening her windows for relief from the oppressive summer air:

"But now, because of the smog, we can't open the windows at home or in the car. Only people with air conditioners and fans are spared. It’s actually a bit easier in the street because it’s windy today. But when you are staying in one place or at home, it’s not very comfortable."

Russia is home to more than one fifth of the world's forests, which are crucial to the regulation of the global climate.

Its boreal - or "taiga" - forests of mainly birch, pine, spruce and fir are the world's largest forest region, covering an area about four times the size of India. (Writing by Guy Faulconbridge; Editing by Kevin Liffey)