Two candidates have been confirmed as the contestants to replace Shinzo Abe as Japan's prime minister.
Veteran lawmaker Yasuo Fukuda served under Junichiro Koizumi
The ruling Liberal Democratic Party has announced that veteran politician Yasuo Fukuda will face former foreign minister Taro Aso.
The party will pick Mr Abe's successor on 23 September but dismissed opposition calls for a snap election.
Mr Abe announced his resignation on Wednesday, a move that surprised many and drew public and media criticism.
A day later he was admitted to hospital suffering from a stress-related stomach complaint.
The party has a lower house majority and so its new leader is guaranteed to become prime minister.
The formal deadline for applications for the party presidency, and the premiership, passed at about noon on Saturday.
Mr Fukuda, 71, said on announcing his application: "This is an emergency situation, so I will do what I must do.
Taro Aso wants to stop the LDP "going backwards"
"I have a strong sense that I should do this for the country to move Japanese politics forward."
Mr Fukuda has stressed the importance of good relations with the country's neighbours.
He has criticised visits by previous prime ministers to a contentious war shrine, which China and the Koreas consider a symbol of Japanese militarism.
Correspondents say his opponent, Taro Aso, is more outspoken in support of traditional values and is more likely to focus on Japan's relations with the United States.
"It is my duty to shed the image that the LDP is going backwards," he said.
ROAD TO RESIGNATION
Sept 2006: Shinzo Abe is elected as PM, with long agenda of reforms
Early 2007: Series of scandals involving senior ministers
July 2007: LDP loses control of Japan's upper house for the first time in its history.
27 Aug: Abe reshuffles his Cabinet
9 Sept: Abe stakes his job on extending Japan's support of US-led mission in Afghanistan
12 Sept: Abe announces he is stepping down
Mr Aso, a former foreign minister, had been seen as the leading contender to replace Mr Abe.
But Mr Fukuda could also harness strong party support.
He had been considered a key candidate to replace Mr Abe's predecessor, Junichiro Koizumi, when he stepped down in September 2006, but decided not to stand.
Finance Minister Fukushiro Nukaga, who on Thursday announced his decision to run, backed out and has thrown his support behind Mr Fukuda.
Since Mr Abe's resignation there have been calls for a snap election, as well as concerns over a leadership vacuum while he is in hospital.
Chief Cabinet Secretary Kaoru Yosano said that Mr Abe would remain in charge.
"Although Mr Abe has expressed his intention to resign, the current Cabinet is responsible for affairs until the new prime minister is inaugurated," he said.
Mr Abe's decision to step down followed a disastrous loss for his party in upper house polls in July and a series of damaging ministerial scandals that had led many to question his leadership skills.