Japanese Prime Minister Shinzo Abe was hospitalized for stress and exhaustion Thursday, a day after announcing his resignation, as his party scrambled to find a replacement amid growing calls for a general election.

Abe, 52, was to remain hospitalized for at least three or four days, his doctors said, leaving the care of his scandal-scarred government with his top deputy, Chief Cabinet Secretary Kaoru Yosano.

"He is suffering from extreme exhaustion," said Dr. Toshifumi Hibi at Keio University Hospital. "He has lost weight. Symptoms include abdominal pain, digestion problems and lack of appetite."

Abe, 52, surprised members of his party and even his own Cabinet on Wednesday by deciding to resign only days after he pledged to stake his government on the success of legislation to extend a naval mission providing fuel for coalition warships in the Indian Ocean.

The nationalist Abe, whose government was severely damaged by a string of scandals and his party's loss of control of the upper house of parliament in July elections, said someone more politically viable should shepherd the Afghan measure that the opposition is trying to scuttle.

Chief Cabinet Secretary Kaoru Yosano had said medical problems contributed to Abe's decision. He said Abe had been receiving regular checkups from his personal doctor since returning from a regional summit in Australia earlier this week, but refused to reveal further details.

Abe's resignation, meanwhile, left the troubled ruling Liberal Democratic Party to scramble for a replacement amid growing calls for a general election to give voters a role in choosing the new government.

The front-runner to replace Abe, former foreign minister and fellow conservative Taro Aso, was expected to announce his candidacy later Thursday. Kyodo News reported the Liberal Democratic Party would decide the election schedule on Thursday and campaigning could start as soon as Friday.

Abe's popular predecessor, Junichiro Koizumi, reportedly refused supporters' plea to join the race. But Finance Minister Fukushiro Nukaga, who served as defense minister under Koizumi, said he wanted to run.

Calls for a snap election for the powerful lower house of parliament, which chooses the prime minister, gathered steam Thursday amid the confusion. The opposition took control of the upper house of parliament in elections on July 29, capitalizing on the unpopularity of Abe's scandal-scarred government.

"With the LDP government thrown into this much confusion, the voters should be asked in the proper fashion who their choice for leader is in a general election," the national Asahi newspaper said in an editorial. "That is the only way to bring back politics based on the people's trust."

Abe made no mention of his medical problems when announcing his resignation. But his vague reasons for leaving — that he felt a new leader was needed to unite the ruling and opposition parties — and the awkward timing fueled speculation he was forced out by the LDP leadership and suffered from health troubles.

Abe, whose support ratings in opinion polls had sagged to about 30 percent, has not yet announced a date for his departure.

When he steps down, Abe will leave behind a government known for scandals and gaffes. He is also leaving amid a political brawl over the country's aid to U.S.-led forces in Afghanistan.

Four of Abe's Cabinet ministers have resigned in scandals, including one who quit this month just a week after being appointed. An agriculture minister committed suicide over a money scandal in May.

The Liberal Democratic Party said it would use a streamlined election process to choose his successor as party president, reportedly on Sept. 19. The party leader is guaranteed election as prime minister because the party controls parliament's lower house.

The leadership change came as the government opened its battle in parliament over the Indian Ocean naval mission, which the opposition has vowed to defeat.

Japan's navy has been providing fuel for coalition forces in Afghanistan since November 2001 under an anti-terrorism law that has already been extended three times. The legislation is a key issue before the special parliament session that opened Monday.