Anglo American will sell all of its Australian coal mines after rejecting a takeover bid from rival BHP.

It owns five coking coal mines in Queensland's Bowen Basin — Moranbah North, Capcoal, Dawson, Aquila and Grosvenor. 

Anglo American chief executive Duncan Wanblad said the changes would come in "urgently" and the sale of its Australian assets would be used to "reset" the company's balance sheet.

Anglo American's five operations employ about 5,000 workers plus contractors, according to the mining union. 

The 107-year-old London-based company said the move would "create uncertainty for its workforce", however there had been "strong buyer interest" in the high quality assets.

Earlier this week the London-based mining group knocked back BHP's $64.6 billion offer, saying it undervalued the company.

The announcement is "unnerving" for the small communities like the rural town of Middlemount which are "fundamentally wrapped up" with the mines, Isaac Mayor Kelly Vea Vea said. 

"This announcement is about more than just mining leases. We've got 600 homes, community infrastructure, water supply, social services like childcare and health that are all fundamentally wrapped up with these mines," she said.

Any sale would have to consider the infrastructure attached to the mine, she said. 

"It will make a huge impact on the livability of our communities if that is not maintained.

"We would expect that community wellbeing really be at the forefront of any discussions between companies, state governments and local government."

Steven Boxall from Mackay's Resources Centre of Excellence said there may be bumpy road ahead but expected the mines would sell fast given the high prices of steelmaking coal.

Mr Boxall said coal mine sales were not new and BMA and BHP had divested in the last couple of years.

"When you look at Stanmore, Whitehaven and Bowen Coking Coal, there's a new wave of operators coming through picking up these assets, and they're potentially able to operate them a little bit more efficiently without the head office costs and overheads," he said.

Minerals Council of Australia chief executive Tania Constable said the shift was not unexpected and job loss was unlikely in the short term.  

"We expect that those jobs will be retained in the short-medium term future and that offers great opportunity and a lot of money flowing into Queensland," she said. 

On Tuesday, Anglo American announced it would also sell or demerge its De Beers diamond business and Anglo American Platinum operation. 

It's focusing instead on copper, iron ore and crop nutrients and southern African and South American markets. 

Mr Wanblad said it "marks a major new phase in executing their strategy to make a "radically simpler business".

Mining and Energy Union general vice president Steve Smyth said the decision to divest caught the union by surprise. 

"We would have thought they're world class metallurgical coal assets in Queensland they'd want to hang onto, these assets have made them a lot of money and a lot of profit over a lot of years," he said.

Mr Smyth said new smaller industry players were welcome so long as they "behave" and continue to maintain the community infrastructure attached to the mines. 

"That's all got to be factored into it as well and that's what the union is calling on, that whoever purchases these assets they guarantee that communities will continue to thrive," he said.

He said there was "a little bit of uncertainty" for workers about what would happen next. 

"Some of them have raised concerns about what it means for them and their future — there's a little bit of uncertainty," he said. 

"We're calling on all levels of government to ensure that Anglo are held to account."