Workers at Japanese manufacturers averaged 13.4 hours of overtime in August, up 11 percent from a year earlier for the fourth consecutive monthly rise, the Health, Labor and Welfare Ministry said Monday in a preliminary report.

“Bright signs are seen for the economy as production activity is gaining momentum,” a ministry official said, “although the overtime increase is partly attributable to a fall in the number of employees.”

Overtime work in the manufacturing sector is seen as a key indicator of economic activity.

Average overtime hours for all industries, including manufacturers, rose 1.5 percent from a year earlier to 9.2 hours, up for the second straight month, according to the report, which is based on a survey of companies with at least five workers.

The average nonregular pay, including overtime pay, in all industries rose 0.8 percent to 17,340 yen in August, the survey shows.

But the average regular wage fell 0.8 percent to 260,948 yen, bringing the average overall wage down 0.7 percent to 278,288 yen.

The average for bonuses and other special payments plunged 30.6 percent to 20,180 yen, marking the biggest decline on a preliminary basis since the ministry began the survey in January 1990.

The average overall pay, including bonuses and other special payments, fell to 298,468 yen, down 3.7 percent.