By Tommy Stubbington 

Greek markets continued to wilt Wednesday in the wake of Syriza's election victory.

Stocks and bonds in Greece have been hit hard by fears that the antiausterity party could derail the terms of its financial support from its European partners, resulting in another default on its debt or even an exit from the eurozone.

Bank shares, which are always closely tied to the country's government bonds, were also weighed down by growing fears that Greeks are moving their money outside the country to shelter themselves from the possibility that the country exits the eurozone.

The bonds selloff accelerated Wednesday. Traders said Syriza's postelection rhetoric and choice of a right-wing antiausterity party as its coalition partner have fanned investors concerns that the new government is set for a showdown with its creditors.

Syriza leader Alexis Tsipras on Wednesday reiterated he is ready to negotiate a debt reduction. "The market is pricing in a restructuring of some form," said Richard McGuire, a fixed-income strategist at Rabobank.

"Eventually we think a compromise will be reached with the Troika, but you'd need a very strong stomach to buy into Greek markets at the moment, " he said.

Short-term bonds, a gauge of investors' levels of concern over the possibility of default, sank particularly heavily. The yield on two-year debt rose by 2.63 percentage points, an enormous move by bond-market standards, to 16.5%. Yields rise when prices fall.

Greek bonds maturing in 2019, issued last year at a yield of just under 5%, now yield over 13%. As a whole, Greek bonds are closing in on the highs they hit in early January when markets first began to worry about the prospect of a Syriza victory. Wednesday, Greek stocks are down by 6.2%.

"I don't find it comfortable investing in Greece right now. The risk of restructuring is just too high," said Torgeir Høien, a portfolio manager at SKAGEN Funds who sold all his Greek bonds late last year.

"We have a very peculiar coalition governing the country now. The only thing binding them is their opposition to the terms of the bailout. Any restructuring would be likely to affect privately-held debt," he said.

Stocks tumbled for a third straight day. Athens's main stock index hit its lowest in more than two years. Bank stocks were hit particularly hard, with Piraeus Bank S.A., Eurobank Ergasias SA, National Bank of Greece S.A. and Alpha Bank AE all falling by around 20%.

Outflows from Greek banks accelerated in January, according to a report published by Moody's Investors Service this week, with around 5% of deposits having left the banking system since the end of November.

"The uncertainty has fueled renewed speculation around the risk of a Greek exit from the euro area, and damaged depositor confidence," said Nondas Nicolaides, an analyst at Moody's.

The Greek wobbles dragged down broader European markets, which had started the day with an upbeat tone following a strong finish to U.S. markets overnight. The Stoxx Europe 600 was 0.3% lower midmorning.

Bonds in Italy, Spain and Portugal all declined, giving up part of the gains run up since the European Central Bank last week announced a bond-buying stimulus program.

Safe-harbor German bonds rose, with the 10-year yield falling to 0.36%,

Write to Tommy Stubbington at tommy.stubbington@wsj.com