Despite the lower production last month, Gympie was upbeat about the mine's performance since March, producing 50,000t a month more than budgeted at an average of 200,000t.

Southland set a March production record this year of 225,000t after the company repositioned the longwall back on the seam floor in mid-February.

Gympie managing director Harry Adams said recent levels of production had enabled the company to build up a stockpile of washed coal in excess of 200,000t, which was more than sufficient to act as a buffer against varying levels of production.

However, forecast sales of 500,000t for the June quarter might not be reached after several shipments due in May were delayed due to port congestion.

Adams said in view of these delays, which could occur again in June, it was likely that some previously projected sales will be pushed into early July.

However, he said the colliery was well placed to reach ROM production of 500,000t for the June quarter.

This year has seen a significant turnaround for Southland after months of operational problems last year led to second-half production of only 373,000t.