At least eight miners have been killed in a methane gas explosion in a coal mine in western Ukraine's Lviv region, according to officials.

Twenty other workers were still unaccounted for after the blast in Stepovaya mine, the country's emergencies service said in an online statement on Thursday.

Thirty-four miners were at a depth of 550 metres when the explosion ripped through the mine at 12:46 local time (13:46 GMT), the statement added.

The mine, which is run by the state company Lvivvuhillja, is located 460km west of the capital, Kiev, and about 10km from the Polish border.

In a post on Facebook, Oleksandr Volynets, head of a miners' union, put the death toll at 11.

Ukrainian presidential spokesman Svyatoslav Tsegolko said in a separate statement that rescue operations were ongoing.