SYDNEY (BLOOMBERG) - A third senior Australian government lawmaker announced he is quitting politics, in a further blow to Prime Minister Scott Morrison ahead of elections expected in May.

Indigenous Affairs Minister Nigel Scullion, 62, who has served in the Senate for 17 years, said in a statement on Saturday (Jan 26) he won't stand for re-election.

The announcement came hours after Human Services Minister Michael Keenan, 46, said that after 15 years in Parliament, he couldn't commit to another term.

The father of four cited the "formidable" pressures of family life for his decision.

Last week, Minister for Jobs Kelly O'Dwyer, 41, said she would also step down to spend more time with her two young children.

Morrison is entering a critical period ahead of the election and is attempting to revive the fortunes of his Liberal-National government.

The government lags the main opposition Labor Party by 10 percentage points, according to the most recent Newspoll in December. Should that margin be replicated at the ballot box, the coalition would lose about 20 seats in Parliament and Labor leader Bill Shorten would take office.

Morrison sought to downplay the ministers' announcements and brushed off a question from a journalist who asked whether they were rats leaving a sinking ship.

"I don't think that is a very kind way to put it," he said, speaking to reporters in Canberra. Scullion was retiring, while O'Dwyer and Keenan were stepping down for family reasons, Morrison said.

The government remained focused on delivering "on our plans for a stronger economy", he added.

The loss of three ministers creates the impression among voters that the government "is in its death throes", said Nick Economou, a political analyst at Monash University in Melbourne.

"It confirms for the public that this is a government facing the end," he said.