Indonesia's biggest coal-producing province of East Kalimantan has recorded a spike in coronavirus cases, with miners among those infected, but so far there has been no disruption to coal operations, a local official said.

The Southeast Asian country is the world's biggest thermal coal exporter and has been riding a boom in prices powered by strong demand from countries such as China, South Korea and Japan.

East Kalimantan on Borneo island reported 979 coronavirus infections on Thursday, the highest number outside the densely populated island of Java. The hospital bed occupancy ratio in the province had also reached 73% by Wednesday, health ministry data showed, among the highest levels in the country.

"The spread of Covid-19 in East Kalimatan has reached all areas and not just the urban areas," Andi Muhammad Ishak, a spokesperson at the East Kalimantan Covid-19 task force told Reuters, adding infections had been reported in the mining sector.

"There are quite a lot (of miners infected), but it has not reached a point where they have to stop operations," he said, without specifying where the infections occurred.

Indonesia's central government this week urged regional authorities to act to head off the type of surge of cases that is crippling the healthcare system in parts of Java and prompted a lockdown.

Mine operations at companies such as PT Bumi Resources, the country's biggest coal miner, and PT Bayan Resources, which both have operations in East Kalimantan, were running normally, company officials said.

"Bumi has tried to maintain close to normalcy in production over the last year," director Dileep Srivastava said. "In 2021, our volume guidance is unchanged at 85 million tonnes to 89 million tonnes."

Srivastava said Bumi continued to implement strict health protocols for its employees, including regular screening and immediate contact tracing to contain any risk of the virus spreading to other employees in the even of an outbreak.

He also said that most Bumi employees were vaccinated.

Bayan director Jenny Quantero said the company was operating in "full force" and had started vaccinations for all employees working at the mine sites.

Bayan is keeping its 2021 production guidance of 32-million to 34-million tonnes.