"The recovery is there but it is weak, modest and fragile, meaning that there are several risks - financial, economic, geopolitical, political - that could undermine easily this recovery," the ECB chief warned in Frankfurt.
"It is still premature to declare any victory," Draghi said.
Falling sovereign yields help to boost economies, spilling over into cheaper loans for business while easing the pressure on governments to impose yet tougher austerity measures on their people.
Portugal, which hopes to exit its 78-billion-euro (A$119-billion) bailout program on May 17, returned to the market on Thursday.
It raised 3.25 billion euros in a sale of five-year government bonds to investors via a syndicate of investment banks, the first such deal in a year.
Demand for the Portuguese bonds outstripped supply by more than three-to-one, a banking source said. The rate of return was not immediately divulged.
In day-to-day trading, however, Portugal's five-year yield eased to 4.022 per cent in the late afternoon from 4.088 per cent the previous evening while the 10-year yield fell to 5.352 per cent from 5.412 per cent.
Spain's borrowing costs plunged in its first major debt auction of 2014 as it raised 5.3 billion euros in five- and 15-year bonds. The five-year rate dropped to just 2.382 per cent from 2.697 per cent three weeks earlier.
Day-to-day trading on the secondary markets was more dramatic, with the Spanish five-year bond yield plunging as low as 2.213 per cent - the lowest since it joined the single currency - from 2.326 per cent the evening before.
Spain emerged timidly from recession in the third quarter of 2013, with official data showing growth of 0.1 per cent, but the unemployment rate remains painfully high at about 26 per cent.
Just two days earlier, Ireland took a major step on the road to economic recovery with its first bond issue since exiting its international rescue program.
"Ireland, Portugal, Spain are racing ahead because they have done their homework, they have had their bailouts, they have had their reforms, they had them early," Christian Schulz, senior economist at German private bank Berenberg.Schulz told AFP.
"Italy is following, it had its reforms a bit later than the rest and maybe not as strong as the rest," he added.
-AAP