"The situation is tough. The angry waves of the Democratic Party are attacking all over Tokyo," he told a news conference.
"If this momentum continues, there is a risk of one-party despotism."
Yosano, himself facing a fight to hold onto his constituency in the Japanese capital, criticised the opposition's spending plans saying the DPJ will find it hard to keep its promises "as fiscal conditions are tough".
At the same time other members of the ruling party have tried to play down the polls, including the prime minister who in a televised appeal on Tuesday said: "Our party is the one that has the responsibility to govern."
Aso, who cast his ballot early on Tuesday ahead of Sunday's election, sought to convince voters that only an experienced LDP leader can handle Japan's struggling economy and security threats from neighbours like North Korea.
In the latest survey to forecast a ruling bloc loss, the Sankei newspaper forecast on Tuesday that the DPJ would win 300 seats in the powerful 480-seat lower house of parliament, ending half a century of almost unbroken LDP rule.
The paper said the LDP could see its number of seats more than halved to around 130 while its junior partner, the New Komeito, would have trouble keeping its current 31 seats.
But it also said the situation was fluid with more than 30 per cent of voters still undecided.
|Opinion polls predict the DPJ led by Yukio Hatoyama will win big on Sunday [AFP]
A landslide victory for the opposition would be almost the mirror image of the 2005 election results when popular leader Junichiro Koizumi led the LDP to a huge victory with promises of market-friendly reforms.
Since then Japan has had three more prime ministers and support for the LDP has sagged due to scandals, policy flip-flops and a perception that the party has failed to address the deep-seated problems of a shrinking, fast-ageing population.
Yukio Hatoyama, the leader of the opposition DPJ, is proving to be increasingly popular among voters and has vowed to bring change to Japanese politics.
He promised to put Japan on the road to recovery by boosting consumer spending, freezing tax hikes and adopting a diplomatic stance less subservient to the United States.
The opposition says it could fund the steps mostly by cutting waste.
But analysts worry the DPJ's promises to increase household spending such as child allowances, toll-free highways and aid for farmers might inflate a public debt already equal to 170 per cent of Japan's gross domestic product.