The miners were trapped on Monday by a rock fall at the Pioneer gold mine. The mine, one of Russia's largest, is located in the Amur region which borders China, about 5,300 km (3,300 miles) east of Moscow.

"The situation remains difficult," Amur Governor Vasily Orlov said on Telegram. Orlov said that specialist mine rescuers had flown in from Russia's vast coal region, the Kuznetsk Basin known as Kuzbass, and other Siberian regions.

He said hundreds of rescuers had cleared swathes of rubble and rock and that they were pumping out water. There was no contact with the trapped miners.

Orlov said that rescuers had decided to drill down through several hundred metres of rock to where the miners are, in an attempt to assess their condition and establish contact.

President Vladimir Putin has been informed of the situation and ordered that every effort be made to save the miners, the Kremlin said on Tuesday.

Russian emergency services said on Wednesday that the volume of rubble and rock at the mine was nine times larger than previously estimated, the RIA state news agency reported.

The mine is owned by sanctions-hit Russian copper and gold producer UMMC.

(Writing by Guy Faulconbridge in Moscow; Editing by Mark Trevelyan)