In addition, she said U.S. has to sort out its budget dispute between Congress and President Barack Obama. Up against a New Year's deadline, the two sides put off much of their dispute for a few months.
"Good decisions have been made," she said. "Sometimes at the last minute, as in the United States, sometimes laborious and confusingly as in the eurozone," she said. "In 2013 they have to keep up the momentum.
Angel Gurria, the secretary general of the Organization for Economic Cooperation and Development, echoed Lagarde, saying "let's fight complacency with everything we've got, let's continue with the reform process so we can consolidate this hesitant recovery."
Akira Amari, Japan's minister of economic and fiscal policy, underlined the determination of the newly elected government of Prime Minister Shenzo Abe to jolt the country's economy out of its stagnation.
And the head of Canada's central bank, Mark Carney, said the world's major economies, so far supported by central bank stimulus such as low interest rates, needed to "achieve escape velocity" in which growth becomes self-sustaining. Carney, who is due to become governor of the Bank of England in June, said the eurozone had been stabilized by an offer by the European Central Bank to buy government bonds of indebted countries and lower their borrowing costs.
Yet Carney said the ECB move was "crucial but not decisive" without progress on banking union and reforms to increase growth.
He said policy makers "have to finish the job they have started."