As heavy rains slowly subside in central Queensland, giant global mining firm Rio Tinto Ltd gradually returned to its mining activities in the region, following the incessant downpours during the past few days that transformed the area's mining pits into temporary dams.

Rio Tinto told Reuters on Wednesday that the continuous rains seen on its mining sites in the region "has impacted on production at our Queensland operations," though it clarified that no final assessment has been made on the effects brought by the weather disturbance.

Despite the flooding, Rio Tinto has decided to partially resume its mining operations disrupted activities following the weekend wet weathers as it added that work is now underway to determine the extent of impacts.

Media reports revealed that the unusually heavy downpours significantly disrupted the operations of up to 40 open-cut coal mines in Queensland and mining authorities in Bowen Basin and nine other mining areas have already declared natural disasters.

As early as last week, Macarthur Coal sued for force majeure as continuous rains depleted the miners' stocks of steel-making coals on its Coppabella and Moorvale mining sites.

Mining firms usually resort to force majeure declaration when unexpected incidents affect production activities and force them into reneging on their legal obligations.

A Reuters report said that the Macarthur declaration was still in force as of Wednesday though it indicated that Rio Tinto's operations were resumed due to the mining firm's much wider mining activities in the Bower Basin area.

Meanwhile, the Queensland Resources Council (QRC) warned that the non-stop downpours could significantly reduce the state's annual mining output of $38 billion as QRC head Michael Roche told ABC that some $3 billion could be taken away monthly if the bad weather continues.

Roche also warned that the prolonged wet season could deplete mining companies' current stockpiles of coal and negatively affect their ability to meet export obligations.