“We have advised customers that we are engaging with authorities who are working on re-establishing regular and safe border crossings,” a spokesman for the miner said in an email on Wednesday.

The virus outbreak that began in China and prompted a lockdown that has weighed on the Chinese economy has sparked concerns about metals demand in the world’s top copper consumer.

Transport restrictions have been imposed to stop the spread of the virus.

Mongolia said on Monday it would suspend deliveries of coal across its border into China until March 2 and had already stopped foreign nationals entering via China.

Yunnan Copper (000878.SZ), part of state-owned Chinese metals group Chinalco, takes almost 10,000 tonnes a month of copper concentrate, or partially processed copper ore, from Oyu Tolgoi for its Chifeng smelter in China’s Inner Mongolia region, a source at the company said.

Like other Chinese smelters, Yunnan Copper is struggling with high inventories of byproduct sulphuric acid amid the virus lockdown and has cut copper output at the 400,000 tonnes per year Chifeng plant by 30%, said the source, who declined to be named as he is not authorised to speak to media.

The source said Yunnan Copper was currently unable to take concentrate from the Mongolian border to the plant via truck but the situation is “getting better”.

Yunnan Copper did not immediately respond to a request for comment.

Reporting by Tom Daly and Melanie Burton; Editing by Jason Neely and Edmund Blair