European Central Bank president Mario Draghi on Thursday said the bank would not bring its massive bond-buying scheme to an abrupt end, reassuring markets as it took a first step towards scaling back extraordinary stimulus.

"The decision today is for an open-ended programme," Draghi told reporters after the ECB announced it would halve its bond purchases to 30 billion euros a month from January until September.

"It's not going to stop suddenly, it's never been our view that things should stop suddenly," he added.