With its first purchases of government bonds under its enhanced stimulus plan, the European Central Bank (ECB) showed it's willing to be patient in its efforts to reignite the euro area's economy.

The ECB and national central banks started buying sovereign debt on Monday under the 19-month plan to inject 1.1 trillion euros (US$1.2 trillion) into the economy. While purchases included bonds from at least five countries, the size of individual trades—at between 15 million euros and 50 million euros—was small relative to the program's goals, according to people with knowledge of the transactions.

“The amount bought may be small to start with, but this will be like a pressure cooker,” said Ciaran O'Hagan, head of European rates strategy at Societe Generale SA in Paris. “They have just switched on the heat and we will need some time for the pressure to mount.”