A major rift opened up in Australia's fragile ruling coalition on Friday as Deputy Prime Minister Barnaby Joyce refused to quit over an affair with a staff member, and derided Prime Minister Malcolm Turnbull's condemnation of his behaviour as inept .

Australia's Deputy Prime Minister Barnaby Joyce

Sydney:

Turnbull, whose coalition holds a razor-thin majority of just one seat, said on Thursday Joyce, had shown a "shocking error of judgment" for conducting the affair with his former press secretary, who is now pregnant, and called on his deputy to consider his position.

The comments were seen as a thinly veiled call for the National Party leader to resign from cabinet, but Joyce, a married father of four who had campaigned on "family values", said on Friday he had the support of his colleagues to continue.

Joyce leads the rural-based National Party, the junior partner in the centre-right government led by Turnbull's Liberal Party, a political alliance that has existed since 1923.

"Comments by the prime minister yesterday at his press conference, I have to say that in many instances, they caused further harm," Joyce told a press conference in Canberra, wearing his trademark bushman's hat.

"I believe they were in many instances inept and most definitely in many instances unnecessary... All that is going to do is basically pull the scab off for everybody to have a look at."

Turnbull refused to comment on Joyce's criticism but the public spat fuels pressure on the prime minister to sack his deputy, which would put the government's one-seat majority at risk should he choose to leave parliament.

The Senate on Thursday passed a motion for Joyce to resign over the affair, saying he had breached standards of behaviour expected of a minister.

Although lawmakers had previously been reluctant to criticise Joyce, a plain-spoken small-town accountant turned politician, he has come under pressure following revelations that his former staffer was given two highly paid jobs after leaving his office.

"This government is in crisis. The Prime Minister and Deputy Prime Minister are at war with each other. This crisis cannot be allowed to continue. Malcolm Turnbull must sack the Deputy Prime Minister from the Cabinet," said Bill Shorten, leader of Australia's main opposition Labor Party.

Eager to draw a line under the scandal, Turnbull said he will change the ministerial conduct rules, new standards broadly similar to a ban on relationships between lawmakers and staffers adopted last week by U.S Congress.

Unlike the U.S. rules, the Australian rules currently only relate to cabinet ministers and their direct subordinates, leading to criticism of the changes.