Portugal's financial markets are in turmoil amid growing concerns over the future of the country's coalition government and its ability to pursue the austerity measures demanded by creditors.

While the country's main PSI 20 stock index tumbled 5.4 percent to 5,233 soon after the open Wednesday, the yield on Portugal's benchmark 10-year bond spiked 0.22 percentage point to 6.94 percent. Both are signs of growing investor unease.

The latest bout of unease were triggered by the resignation of two ministers this week over tough budget cuts that have sharply reduced living standards in one of the poorest countries that uses the euro. On Tuesday, Prime Minister Pedro Passos Coelho defied calls to resign.

Portugal is implementing austerity measures in return for its 78 billion euros ($102 billion) international bailout.