The German economy, the biggest in the 12-country euro zone, is growing at its fastest rate in four years, data showed on Thursday, in a welcome piece of news for the government ahead of crunch regional elections later this month. But experts said that the data were likely to turn out to be a flash in the pan and recovery was already losing momentum. German gross domestic product (GDP) expanded by 1.0 percent in the period from January to March, compared with the preceding three months, the federal statistics office, Destatis, calculated in preliminary figures. That was double analysts' expectations for first-quarter growth of just 0.5 percent and was, in fact, the fastest quarterly rate of growth since the first quarter of 2001. On a 12-month basis, too, GDP expanded by a "good one percent" when taking into account that there were two fewer working days this year than in the first quarter of 2004, Destatis said.