Italian Prime Minister Silvio Berlusconi has warned members of parliament they risk plunging Italy into the middle of the eurozone's debt crisis if they vote against him in a confidence vote tomorrow.

Speaking in parliament a day before a showdown that could force him from office and trigger early elections, Mr Berlusconi said his government had kept Italy out of the crisis but that the threat of instability remained.

'It is madness to initiate a crisis without any foreseeable solutions,' he said in a speech to the Senate.

The government can be assured of a majority for a confidence motion it has called in the Senate.

But the outlook in the lower house, where the opposition has brought its own no-confidence motion on the same day, is less certain and could be decided by one or two votes.

Some commentators estimate a result as close as 314 votes for Mr Berlusconi against 313 for the combined opposition is possible.

The prime minister can no longer count on a lower house majority following a split in July with former ally Gianfranco Fini and a group of supporters who broke away from the ruling PDL party and formed a centre-right group of their own.

But the result of Tuesday's vote is finely balanced after days of intense lobbying to persuade wavering rebel deputies to support the government.

Mr Berlusconi said if he defeated the no-confidence motion, he would open up his government to other forces from the centre and centre-right, in an appeal to so-called 'doves' in the rebel camp not to bring the government down.

His leadership credentials have been undermined this year by scandals that forced three members of the government to resign, an uproar over his fondness for parties and young women and a scandal over garbage collection in Naples.

Speaking to reporters earlier, the 74-year-old premier said he was confident he had the numbers to survive the vote.

'I am serene, optimistic and confident as I always am,' he told reporters as he went into a cabinet meeting that will sign off on the Senate confidence motion.

Tomorrow's vote will be closely watched on financial markets on high alert over the eurozone debt crisis, and a prolonged period of uncertainty or a divisive election campaign could turn the spotlight on Italy's strained public finances.

Despite one of the heaviest debt burdens in the world at almost 120% of gross domestic product, Italy has largely escaped the turmoil seen in Greece and Ireland thanks to tight control of public spending and a conservative banking system that avoided excess during the market boom.

Even if Mr Berlusconi scrapes through, there is little confidence he will have the strength to push through the kind of reforms authorities such as the Bank of Italy believe are needed to address deep-seated problems in the economy.

An alarming jump in the premium investors demand to hold Italian debt rather than benchmark German bonds last month underlined the danger, although the interest rate spread has since come back from the record levels it hit on 30 November.