CANBERRA (REUTERS) - Australian Prime Minister Scott Morrison's Liberal Party suffered a major upset in New South Wales state's by-elections, preliminary reports indicated on Sunday (Feb 13), presenting a challenge for his ruling coalition ahead of federal elections due in May.

Liberal Party leaders at both state and federal level have come under pressure in recent months over their handling of the latest wave of the Covid-19 pandemic, as cases and deaths soared following the arrival of the Omicron variant.

Official tallies of the four by-elections will not come for weeks until mail-in votes are counted, but New South Wales Premier Dominic Perrottet has conceded the Liberals will lose a seat which has never been won by the opposition Labor Party.

The loss of the regional seat of Bega, in the state's south, has pushed Perrottet's government further into minority. It has also sent a potential warning to Morrison who must call federal election by May 21.

Perrottet said the government of New South Wales, Australia's most populous state, will take lessons from the "disappointing" results.

"There (are) certainly messages for us to look at in terms of what we are doing on the ground," Perrottet said at a news briefing.

The Liberals also suffered a swing against them in former state Premier Gladys Berejiklian's seat.

Anthony Albanese, the leader of the Labor party, called the results "outstanding".

Keith Pitt, Australia's resources minister, played down the implications of results for the Morrison government, telling told Sky News on Sunday that "these things don't reflect into a federal result".

A January poll showed Morrison's Liberal-National coalition government took a hit after their handling of the Omicron-driven coronavirus outbreak fuelled a backlash, putting Labor into a leading position.