Japan's 0.9pc growth in the first quarter could just be a "sugar high" following the government's massive stimulus measures, former World Bank president Robert Zoellick has said.
Japan posted 0.9pc quarter-to-quarter growth in the three months through March, during which time Prime Minister Shinzo Abe took charge with a platform that has featured ramping up money supply and intense fiscal stimulus.
"On the one hand, I think it's understandable that Prime Minister Abe would come in and try to have some shock effect. But no one should be under the illusion that this isn't a big if," said Mr Zoellick, whose term ended last year.
"What I would watch... [is] how do you make sure that it isn't just a sugar high? How do you make sure that there is a follow-through?" he told a forum on relations between the US and New Zealand.
Mr Zoellick, who also served in senior positions in former US president George W Bush's administration, said Japan already had a debt problem and needed to go through structural changes to liberalize its economy.
He voiced hope Mr Abe's move to enter talks on the emerging Pacific-wide free trade deal, the Trans-Pacific Partnership, was a way to force Japan into taking politically risky reforms, AFP reported.
"If Japan doesn't undertake those structural reforms, either through its own policies or through the TPP or both, I worry that this will primarily be a currency devaluation strategy - and that has dangers for others," he said.
The yen sank this month to more than 100 to the dollar for the first time in more than four years. The weaker yen benefits Japanese exporters by making their goods cheaper but has prompted criticism by some competitors.
Japan's first-quarter growth - which would be 3.5pc if the data were on an annualized basis - came after the world's third largest economy spent much of the past two decades stuck in low growth or worse.
The "Abenomics" plan has drawn increasing interest in Europe, where some critics of austerity plans say that Japan may serve as a model to perk up the economically troubled continent.