(WSJ) - Stocks and bonds on both sides of the Atlantic rallied and the euro sank heavily Thursday after the European Central Bank delivered a bigger program of asset purchases than investors had expected.

ECB President Mario Draghi said the central bank would buy €60 billion ($69 billion) of public and private-sector debt every month until at least September 2016, or even later if needed.

“All eyes were on Mario Draghi and he has delivered a bigger bazooka than investors were expecting. This will satisfy markets for now,” said Mauro Vittorangeli, a senior portfolio manager at Allianz Global Investors.

Mr. Draghi’s commitment to pursue quantitative easing until inflation takes a sustained upswing also reassured investors.

“It was a strong statement on inflation. That tells us that QE is going to be with us for quite some time,” said Nick Gartside, chief investment officer for fixed income at J.P. Morgan Asset Management.

Earlier, the ECB kept interest rates on hold at record lows, as expected.

The euro tumbled after the announcement, losing more than 1% against the dollar to trade at $1.1453, an 11-year low. A weaker currency should help boost inflation by making European exports cheaper.

Equity markets in Europe gained. The Stoxx Europe 600 added more than 1% to a fresh seven-year high. U.S. market also turned higher after an early wobble, with the S&P 500 up 0.5%.

“This just means we have more global liquidity, and that’s going to push asset valuations higher,” said Erik Weisman, global bond portfolio manager at MFS Investment Management.

Bonds in the eurozone also rallied sharply, pushing yields in a swath of countries to record lows. German government bonds, considered the eurozone’s safest market, climbed, pushing 10-year yields down to an all-time nadir of 0.37%.