The state-owned company now targets to export at least 10 million tonnes of coal in 2019 and has already secured contracts for 6 million tonnes, according to Commerce Director Adib Ubaidillah.

Along with medium-rank coal shipments to South Korea, Hong Kong and China, Bukit Asam also marketed high-calorie coal in Japan, Taiwan, the Philippines and Malaysia, Ubaidillah said.

The change in export focus was partly a result of changing import regulations in China, Ubaidillah said.

"China has started restricting (imports) now, so in 2018 our strategic marketing reached (markets) that we haven't explored much," he said.

"We are trying Bangladesh and Sri Lanka where economic growth is improving."

Bukit Asam produced 19.7 million tonnes of coal in the first nine months of this year, compared with 16.9 million tonnes in the same period in 2017.

"This shows that in the middle of a volatile coal market we are still surviving," said Arifin.

The company hopes to increase coal output by 5 percent in 2019, he said.

Bukit Asam, whose mines are mostly in Sumatra, supports the recent government restrictions on coal hauling on public roads there, Arifin said.

The policy is "positive for the community" which was not comfortable about coal trucks on roads, Arifin said.

"These are public roads with limited capacity," he said, adding that Bukit Asam did not use public roads for hauling.

However, "the challenges are complicated for transportation in Sumatra," Arifin said, adding that the company wanted to expand its mine concession portfolio into other areas.

"If there are appropriate areas outside Sumatra, like in Kalimantan, we are interested in managing mine (areas) formerly in coal contracts of work," he said.

Arifin referred to the approaching expiry of several large coal mining contracts of work, and rules limiting concession sizes under new special mining permits.

(Reporting by Wilda Asmarini; Writing by Fergus Jensen; Editing by Subhranshu Sahu)

By Wilda Asmarini