The leaders of both of Australia's major political parties agreed on Tuesday that gay people don't go to hell because of their sexual orientation, as Christian beliefs rose to extraordinary prominence in the final days of an election campaign.

Prime Minister Scott Morrison opposed gay marriage while opposition leader Bill Shorten argued for marriage equality ahead of a national vote in 2017 that led to Australia legally recognising same-sex unions.

Mr Morrison, a Pentecostal Christian, accused Mr Shorten, a Catholic before converting to his second wife's Anglican faith, of a "desperate, cheap shot" ahead of elections on Saturday by challenging the prime minister to say whether he believed homosexual people went to hell.

Mr Morrison said he did not believe gay people went to hell, after failing to directly answer the same question from a journalist a day earlier.

"I'm not running for pope, I'm running for prime minister," Mr Morrison told reporters. "So... theological questions, you can leave at the door."