The manufacturing production index dropped 5.13% in March from a year earlier, falling for the 18th consecutive month, the Industry Ministry said on Tuesday, missing analysts' expectations.
The drop in factory output was due to slow auto production, a contraction in exports and household debt, a senior official said.
The figure compared with a forecast 1.9% year-on-year fall for March in a Reuters poll, and followed an revised decline of 2.79% in February.
Factory output for the three months ending in March fell 3.65%, but there were signs of recovery, Warawan Chitaroon, director general of the Office of Industrial Economics told a press conference.
"Orders at the motor show were higher this year, which is a positive sign," she said, adding the recovery in tourism and deployment of the government's delayed 2024 budget would spur manufacturing.
Orders at the annual motor show earlier this month rose 28% from last year.