Five candidates battle to succeed Japan PM Naoto Kan
Five candidates have put themselves forward to succeed Japanese Prime Minister Naoto Kan, and become the country's sixth leader in five years.
Trade Minister Banri Kaieda has become a front runner after winning the backing of a powerful power broker in the governing party.
Opinion polls show former foreign minister Seiji Maehara is the most popular candidate among the public.
Mr Kan is stepping down after just 14 months in charge.
He has been criticised for failing to show leadership after the devastating 11 March earthquake and tsunami, and ensuing nuclear crisis.
The five will spend the weekend making speeches and debating, before the 398 lawmakers in the ruling Democratic Party of Japan (DPJ) vote for a new leader on Monday.
The leader will become prime minister once approval is given by the Diet, or parliament.
Tough challenges ahead
The race is shaping up to be a battle between factions for dominance of the DPJ, the BBC's Roland Buerk in Tokyo reports.
Mr Kaieda, 62, shot to the top of the frontrunner list after winning the backing of Ichiro Ozawa, head of the party's biggest faction.
While Mr Ozawa is a divisive figure who faces trial on charges of misreporting political donations, he is still thought to hold sway over more than 100 members of the Diet, our correspondent adds.
But Mr Kaieda's victory is not assured.
Colleagues have been quoted in the Japanese media as saying his biggest weakness is "indecisiveness", and he was mocked last month for sobbing in parliament while being questioned about the confusion over restarting nuclear reactors idled after the Fukushima disaster.
Seiji Maehara - the public's favourite - would, at 49, become Japan's youngest leader since World War II. He stepped down as foreign minister in March after receiving an illegal $3,000 (£1,810) political donation from a foreign national - an ethnic Korean living in Japan.
Another one-time front-runner is the fiscally-conservative finance minister Yoshihiko Noda, 54, but he is hindered by the fact he shares a factional support base with Mr Maehara.
The remaining two candidates are farm minister Michihiko Kano, 69, and former infrastructure and transport minister Sumio Mabuchi, 51.
Whoever wins the race faces a tough task ahead.
They will have to oversee the biggest reconstruction effort in Japan since WWII and resolve the nuclear crisis at Fukushima where reactors are still leaking radiation.
They will also have to persuade the markets that Japan can overcome a divided parliament to address the biggest national debt in the industrialised world, our correspondent says.