Japan's Prime Minister Junichiro Koizumi has been returned to power but with a reduced majority.
The opposition had hoped for a high turnout
Projections, by public broadcaster NHK, showed his coalition had surpassed the 241 seats needed to retain control of the 480-seat House of Representatives.
But the final total was 275 - 12 below their current strength.
The opposition Democratic Party (DPJ) looked like making major gains, boosting its seats from 137 to more than 170.
Surveys indicated turnout was behind the last lower house elections in 2000.
Mr Koizumi was seeking a second term in office to complete the economic reforms he began more than two years ago.
His Liberal Democratic Party (LDP) had faced a strong challenge from the DPJ.
The party's leaders accepted the early outlook was tough.
"As the largest party, we should be striving to achieve a single-party majority," said LDP secretary-general Shinzo Abe.
"But if the three parties of the ruling coalition achieve a majority, I will take that as a sign of having won the public's trust."
This was the first test of Mr Koizumi's economic reforms since he came to power more than two years ago.
Mr Koizumi's main challenger, Naoto Kan, argued that the LDP was too closely tied to vested interests in the banking, construction and agricultural sectors to carry out real reform.
If the DPJ reach their target of 200 seats in parliament they will be seen as a credible alternative to the LDP, says the BBC's Jonathan Head in Tokyo.
This would give Japan its first genuine two-party political system.
Mr Kan was delighted with the early results. "I can barely speak," he said.
"I hope this will lead to a change in government but we must wait until all the votes are counted," he added.
Our correspondent said both parties campaigned on a platform of economic and political reform, and many people found it hard to distinguish between the policies on offer.
An estimated 40% of voters were undecided and turn out at the polling booth was low - not helped by grey skies and light rain.
However, the first signs of an economic recovery in Japan may have been enough to persuade many uncommitted voters to back another LDP term in office, our correspondent adds.