The nation's coincident index stayed below the boom-or-bust line of 50 percent for the 13th straight month in January, according to a government report released Thursday.

The key economic gauge is expected to log an upward turn soon, however, given the ongoing progress in inventory adjustment, the Cabinet Office said in its preliminary report.

The coincident index stood at 33.3 percent in January, up from a revised 20 percent in December. Any reading below 50 percent is considered to be a sign of economic contraction, while any figure above this line is viewed as a sign of expansion.