Portugal's government teetered on the brink of collapse Wednesday, sending financial markets around Europe into a tailspin and reigniting concerns about the euro area's strategy for dealing with its prolonged financial crisis.

Prime Minister Pedro Passos Coelho defied calls to resign late Tuesday but he was running out of options to keep his center-right coalition government together following the back-to-back resignations this week of two key ministers in a spat over austerity.

If the governing coalition collapses, the ruling party would not have enough votes in parliament to pursue the reforms required to keep accessing the international bailout loans it depends on to avoid bankruptcy. That would put Portugal back to the front and center of Europe's debt crisis, a spot it hasn't held since it was bailed out in 2011.

"Portugal is now the key event risk to watch in the eurozone," said Holger Schmieding, an analyst with German bank Berenberg.

Portugal agreed on the 78 billion euro ($102 billion) bailout program with its fellow euro countries, the European Central Bank and the International Monetary Fund two years ago when it could no longer afford to pay its way on the international debt markets. In return for the loans, and to keep debt under control, Portugal had to agree to a series of harsh cuts and reforms.

The country also has to keep a grip on its finances so that it is able to return to the international debt markets once the current bailout loans run out in June 2014. If investors feel that Portugal is still a risky bet then and charge sky-high rates to buy the country's bonds, the government will be forced to ask for another bailout loan. Worse still, it could also be forced out of the eurozone.

Portugal's austerity program has already proved a massive drag on the economy, eroded standards of living and drawn criticism from trade unions and business leaders.

The effects of austerity programs imposed on Portugal — and the other bailout program countries of Cyprus, Ireland and Greece — have also hit growth across the whole eurozone. The region's economy is currently in its six straight quarter of negative growth and unemployment is at 12.2 percent. This, in turn, has also slowed the global economic recovery.

Signs of hardship are all around in Portugal. Main streets are full of boarded-up stores and restaurants after the government hiked sales tax to 23 percent from 13 percent. Income tax hikes this year have cost many middle-class workers more than a month's pay. Charities report record numbers of requests for food aid, while the European Commission forecasts further declines in household income this year and next.

Unions are currently fighting the government's plans to increase the working time of state employees to 40 hours a week from 35; raise their monthly pension deductions while lowering their pension entitlements; and lay off some 50,000 government workers out of the total of about 583,000.

Worries about the stability of Portugal's bailout plan sent the country's main PSI 20 stock index down 5.45 percent to 5,177 in afternoon trading Wednesday, with bank shares falling up to 13 percent. Stock indexes across the rest of Europe also fell on what was happening in Portugal, with Germany's DAX down 1.5 percent and Spain's IBEX off 2.12 percent.

Another indicator of investor confidence in a country, the interest rate on Portugal's benchmark 10-year bond jumped 1.28 percentage points to 7.74 percent. The rate, which is what Portugal would pay to borrow 10-year money, is far above the 5.23 percent rate it hit in May but nonetheless lower than the 9.77 percent it was at this time last year.

Though the higher rates are not an imminent threat — since the government is not relying on bond markets but surviving on bailout loans — they reflect concerns the country will be unable to get back on its feet once the program ends in 2014.

The crisis in Portugal was sparked by the country's Foreign Minister, Paulo Portas, who is also the leader of the junior party in the coalition. He quit on Tuesday in protest against plans to continue with the tax hikes and pay and pension cuts.

The previous day, Finance Minister Vitor Gaspar walked out, saying he lacked political and public support for his austerity strategy.

Passos Coelho, the prime minister, said in a nationally televised address that he will fight to keep his Cabinet together, "but resolving the problem doesn't only depend on me." (AP)