A think tank reported Monday that the Japanese economy is estimated to have grown a real 2.4 percent in the January-March period from the preceding quarter, due chiefly to a rise in personal consumption.

The Japan Research Institute, a Sumitomo Bank affiliate, said that thanks to the estimated high quarterly growth of gross domestic product, annualized at 9.9 percent, the economic growth for the full fiscal 1999 to March 31 is estimated to have surpassed the government's projection of 0.6 percent.

The think tank did not say by how much, however. It also said it cannot conclude the economy has achieved a sustainable recovery, as there were unusual factors in the January-March quarter.

Japan's GDP for the October-December quarter of 1999 contracted a real 1.4 percent compared with the June-September quarter, which also witnessed negative growth.

Next month, the Economic Planning Agency is scheduled to announce GDP data for the January-March quarter.

The Japan Research Institute estimates personal consumption in the January-March period rose 1.5 percent from the previous quarter.

The estimated rise is because of the Leap Year day in February and because people who refrained from traveling over New Year's due to Y2K restrictions took trips later in the quarter, the think tank said.

Investment in plants and equipment in the January-March quarter is estimated to have gained a mere 0.2 percent from the previous quarter because of a sharp fall from January through March in capital spending by small and medium-size companies.