CANBERRA, April 30 (Xinhua) -- The opposition Australian Labor Party (ALP) leader Bill Shorten has been deemed as the victor of the first leaders' debate of Australia's general election campaign, according to host broadcaster Channel 7.

Shorten was supported by 25 out of 48 undecided voters in the audience while 12 gave it to incumbent Prime Minister Scott Morrison and 11 remained undecided.

In the wide-ranging hour-long debate in West Australia's capital Perth on Monday night, Shorten attacked the government's proposed "tax loopholes" for high-income earners while Morrison sought answers from Shorten on the cost of his ambitious emissions reduction and renewable energy targets.

Shorten conceded for the first time that it is impossible to put a price on his plan to cut emissions by 45 percent from 2005 levels by 2030.

"This issue about 'give us one number' ... I don't think that's possible to do," he said, arguing that a failure to take action on climate change would be a "disaster" for the economy.

Morrison's campaign for re-election has been largely based on economic stability. His Liberal-National Party Coalition (LNP) has promised far-reaching tax cuts for Australians -- a policy Morrison has said is the result of the party's economic management since it won power in 2013.

"We have brought the budget back into surplus and that means we can be relied upon to keep it in surplus and pay down the debt," he said on Monday night.

"As a government, we believe the choice is to lower taxes because we think, as we go into what is going to be a very difficult period ahead, that we've got to get it all very much on track.

"We've got to keep our spending under control, we've got to keep our taxes under control."

Shorten and the ALP have instead campaigned on change and have made significantly more policy announcements than the government, among which are larger tax cuts for low-income Australians, greater action on climate change and greater investment in education, healthcare and infrastructure.

The ALP has also sought to capitalize on the leadership turmoil that has plagued the LNP since 2013, with Morrison being the government's third leader from that time.

"The reality is that in the last six years when you voted for Tony Abbott you ended up getting Malcolm Turnbull, when you voted for Malcolm Turnbull last time you got Mr. Morrison," Shorten said on Monday night.

"The chaos has to stop. But as important as the instability of the current government is the question: is this a strong economy for who? Who benefits at the moment?"