CANBERRA, Aug 23 (Reuters) - Besieged Australian Prime Minister Malcolm Turnbull's leadership looked doomed on Thursday after three of his senior ministers announced they had tendered their resignations and called for a second leadership vote.
The ministers, who supported Turnbull in a leadership ballot on Tuesday against former home affairs minister Peter Dutton, said they had changed their position and now backed Dutton.
Turnbull only won the Tuesday contest by seven votes. Dutton on Thursday publicly called for another leadership vote.
Finance Minister Mathias Cormann, Turnbull's key cabinet supporter who tendered his resignation, said he now believed that Dutton was the best person to lead the conservative government to the next election, due by May 2019.
"I can't ignore reality," Cormann said as he announced he was withdrawing support for Turnbull, adding five other ministers who voted for Turnbull on Tuesday had told him they were changing sides.
"I can't ignore the fact that a majority of colleagues in the Liberal Party... are of the view that there should be a change," he said.
If Dutton's supporters succeed, Turnbull will be ousted without completing three years in power, and whoever replaces him will become Australia's seventh prime minister in a decade.
Turnbull came to power in a party-room coup in September 2015 over former premier Tony Abbott, who also survived an internal leadership contest before his eventual defeat.
A social liberal and multi-millionaire former merchant banker, Turnbull rode an early wave of popular support but he has struggled to appeal to conservative voters and only narrowly won an election in 2016.
The ruling Liberal-National coalition government has consistently trailed the opposition Labor party in opinion polls, but Turnbull has remained the voters' preferred prime minister over Labor leader Bill Shorten.
