The manufacturing production index (MPI) for September fell 4.7% from a year earlier, dragged down by lower production of cars, petroleum and rubber, the industry ministry said on Tuesday.
That compares with a forecast of a 2.05% decline in a Reuters poll, and August's 4.4% contraction.
Capacity utilisation was 63.87% in September, compared with 65.75% in August.
The ministry forecasts the MPI will rise 0.5% this year, after increasing 3.6% last year.