At least nine people have died in forest fires in the Lugansk region of eastern Ukraine near the front line of Kiev's conflict with Moscow-backed separatists, authorities said Thursday.

Some 120 people were evacuated from villages in the region as 1,200 firefighters were dispatched to extinguish the blaze that started Wednesday, the interior ministry said as Kiev tries to determine the cause.

Regional officials said two water-bombing planes and a helicopter were used to tackle the fire that spread over 9,300 hectares.

Emergency services said ten people have been hospitalised and 22 villages were under threat from the fire, which was getting larger due to strong winds.

The Ukrainian presidency said in a statement that it was important to establish the cause of the fire and to establish how it had spread so quickly.

The regional administration said it had temporarily closed a crossing point into separatist-held territory as the fire drew near to a checkpoint.

The blaze spread to just a few kilometres from an area where fighting between Kiev forces and Russian-backed separatists erupts sporadically.

A ceasefire brokered two months ago has largely held and authorities have not said whether the fire has impacted the fighting.

Ukraine has been hit by unprecedented heat waves this year, which have created dangerous conditions for damaging fires that are harder to control.

In July, forest fires in the Lugansk region killed five people and injured around 30 others.

Scientific models predict that changes in climate will increase the frequency and severity of extreme weather events, like catastrophic fires or devastating hurricanes.

Fires earlier this year ravaged more than 66,000 hectares in the exclusion zone around Chernobyl in northern Ukraine, the scene of one of the world's worst nuclear accidents in 1986.