By Tommy Stubbington and Josie Cox 

After a blockbuster quarter for European stock markets, investors are betting there could be more to come.

Tentative signs that the ailing eurozone economy is turning a corner have coincided with the launch of the European Central Bank's bond-buying stimulus program--known as quantitative easing--which has pushed billions of euros into equity markets.

The Euro Stoxx 50--an index of blue-chip stocks inside the single-currency bloc--has surged more than 17% in the first three months of the year to Tuesday's close. Germany's DAX index climbed 22%, its best quarter since 2003. France's CAC 40 enjoyed its strongest three-month run since 2009, rising 18%.

"For Europe, it's been the best of all worlds. The economy has improved at a time when people were too pessimistic, the oil price has supported that recovery, and then along comes QE," said François Savary, who oversees about $10 billion of assets as chief investment officer at Swiss bank Reyl.

The only dark spot has been Greece, where a showdown between the new government and international creditors has rattled investors' nerves, pushing Athens's main index down 6%.

Despite the scale of the rise in most of Europe--which puts a 1% quarterly gain for the U.S.'s S&P 500 firmly in the shade--there is little sign that investors' enthusiasm is waning.

More than half of 908 investors surveyed by Barclays in March said they expect Europe excluding the U.K. to outperform all other regions around the world in the next three months.

"Markets have been running up quite dramatically, but we think that's down to a fundamental improvement in the economy," said Mads Pedersen, head of discretionary asset allocation for UBS Wealth Management, which oversees about $2 trillion of assets.

Private-sector activity in the eurozone grew at the fastest pace in March since May 2011, data showed last week, bolstering a recent upturn in surveys of business confidence.

After several years of no earnings growth, Mr. Pedersen thinks eurozone companies can boost profits by more than 10% this year. This month, UBS Wealth raised its allocation to eurozone equities--already its favorite region globally--after a sharper-than-expected fall in the euro this year further brightened earnings prospects. A weaker currency is good news for exporters and multinationals that get a big chunk of their revenues abroad.

The rapid decline of the single currency, which has slipped more than 11% against the dollar this year, is down to the ECB. The central bank this month kicked off a long-awaited program of quantitative easing, printing EUR60 billion ($65 billion) every month to buy bonds. The aim is to push investors into riskier assets like stocks, as well as weaken the currency, in a bid to stimulate the economy. The early signs are promising.

Bondholders have seen the value of their investments rise rapidly. But new investors face tiny returns now that the ECB has pumped prices up so high. That has sent many private investors into stocks. According to Bank of America Merrill Lynch data, $46.6 billion has flowed into eurozone stock funds so far this year, while $44 billion has left U.S. stock funds.

"This has been an exceptional start to the year for European equities and we're increasingly seeing investors from other asset classes, like fixed income, coming into stocks," said Nick Lawson, a senior equities trader at Deutsche Bank.

The stellar run for Europe's bourses marks a turnaround from the second half of 2014. Then, a slowdown in the economy, as the conflict in Ukraine threatened to weigh down the region's prospects, saw many international investors turn cold on Europe. Now, the greatest weakness of European stocks could lie in their sheer popularity.

A survey carried out by Bank of America Merrill Lynch in March showed bullishness in "uncharted territory" with divergence between U.S. and European stock allocations at its widest since 2007. That means any reversal of fortunes could see a sharp pullback in European stocks as investors throw in the towel.

"There's certainly the risk of some short-term consolidation," said Reyl's Mr. Savary.

But for now, most are happy to stick with Europe's soaring equity markets.

"Whether the rally is sustainable in the long run is going to be dependent on whether the weak euro can convincingly translate into a recovery in earnings," said Philip Lawlor, a partner at London-based Smith & Williamson Investment Management LLP, which manages about GBP15 billion ($22 billion) in assets.

"So far we haven't seen it, but as an optimist, I think it is probably a question of time," he said.

Write to Tommy Stubbington at tommy.stubbington@wsj.com and Josie Cox at josie.cox@wsj.com

UBS (NYSE:UBS)
Historical Stock Chart
From Mar 2024 to Apr 2024 Click Here for more UBS Charts.
UBS (NYSE:UBS)
Historical Stock Chart
From Apr 2023 to Apr 2024 Click Here for more UBS Charts.