Export metallurgical coal production guidance for 2020 has been revised to 19-21 million tonnes from 21-23Mt previously.
Unit costs of production are also expected to increase to about US$70 per tonne from $65/t previously.
An Anglo American spokeswoman told Australia's Mining Monthly that the company had resumed longwall development work at Moranbah North.
"As a precaution, we are adding extensive additional roof supports in the new development area," she said.
"We will also bring forward the planned implementation of further technological solutions."
Annual revenue for Anglo's metallurgical coal division declined from $4.2 billion in 2018 to $3.7 billion in 2019 while earnings before interest tax depreciation and amortization sunk to $1.7 billion from $2.1 billion previously.
"Market prices decreased in line with demand through the second half of the year," Anglo American said.
"Demand was affected by increasingly stringent coal import policies at ports in China and a slowdown in the Indian economy, as well as lower production at east Asian steel mills in response to weaker steel margins."
Production increased 5% to 22.9Mt, owing to a 1Mt production increase at Grosvenor and operational improvements leading to a 10% increase in wash plant throughput.
Those gains were partially offset by the impact of an extended longwall move at Moranbah North.
In addition, there was a strong performance at Dawson where productivity improvements drove an increase in shovel and dragline performance.