The coalition says Labor's tax policies will cost $387 billion extra over the next decade, but Mr Shorten says the figures are wrong.

"The Liberals are lying about tax. I don't want to talk too much about it, that's just a bucket of lies," he told Nine's Today on Friday.

But Finance Minister Mathias Cormann says Labor should reveal their costings if they dispute $387 billion number.

"If they are arguing against that figure, well Bill Shorten may as well argue that boiling water is freezing cold," he told Sky News.

Mr Morrison says the May 18 election is a choice between a strong economy under the coalition and a weak economy under Labor.

"If you can't manage money you can't run the country," he told ABC News.

"When the economy is stronger, then your wages are stronger, your jobs are more secure, your outlook is better."

Both leaders have started their campaigns in Sydney's west, with Mr Shorten visiting a flower market and speaking with small business owners.

Craig Laundy won the seat of Reid, where the markets are located, for the Liberals for the first time ever with a 4.7 per cent margin, but the close Turnbull ally is retiring and Labor has strong hopes of the electorate returning to the fold.

The Penrith-based seat of Lindsay is also in play, with Labor's Emma Husar winning it from the government in 2016 with a 1.1 per cent margin but not recontesting the post after a scandal involving her treatment of staff.

Melissa McIntosh will try to prise it back for the Liberal Party, while Labor is running former NSW state minister Diane Beamer.

Macquarie, on western Sydney's outer fringe, is also expected to receive attention from the prime minister.

Labor on Friday announced an extra $125 million to fund cancer research if the party wins the election.

The leaders have also reportedly agreed to a head-to-head debate in Perth before Australians cast their vote.

Opinion polls are pointing to the coalition losing power to Labor after five-and-a-half years in office.

Australian Associated Press