TOKYO—Toyota Motor Corp. joined other Japanese auto makers on Wednesday in reporting its first increase in monthly domestic output since the March 11 earthquake and tsunami disrupted their global supply chains.

The August gains mark the latest step in the industry’s steady efforts to restore domestic production to pre-quake levels, but executives continue to warn that the strong yen could undermine a recovery of the export-dependent industry.

Toyota, Japan’s largest auto maker by output, posted a 12% on-year rise in domestic production in August, marking its first year-over-year increase in 12 months as a near-complete recovery in its parts supply chain helped boost output.

Suzuki Motor Corp. and Mazda Motor Corp. also said they boosted domestic production in the month.

Suzuki, Japan’s fourth-largest auto maker by volume, said its output in August rose by 5.9% from a year ago, marking its first rise in 11 months, while Mazda, the country’s fifth-largest car company, said its production climbed 5.6%, its first rise in six months.

Nissan Motor Co. and Honda Motor Co.—Japan’s second- and third-largest car makers, reported 17% and 2.5% drops in domestic output in August, respectively.

The companies attributed the declines mainly to higher production a year ago spurred by strong demand by customers who rushed to buy fuel-efficient cars before the expiry of government subsidies.

In the April-July period, Japan’s overall auto output fell 34%, or 1.4 million vehicles, compared with the same period in the previous year. But car makers are now poised to start to boost production to make up for delays after the March disasters.

Toyota added overtime to resume normal output ahead of schedule in September, while Honda plans to lift output volume by 25% in the fiscal second half through March. Nissan expects its output to be back to pre-quake levels in October.

Despite these upbeat plans, Japanese auto makers still face headwinds, with the yen near a postwar record high of ¥75.94 against the dollar and an uncertain global economic outlook casting doubt on the strength of overseas demand.

Nissan Chief Executive Officer Carlos Ghosn last week warned that Japanese car makers could be forced to move more production outside Japan if the yen stays at current levels over the next six months, though he said he believes the yen’s strength won’t last.

Toshiyuki Shiga, the chairman of Japan Automobile Manufacturers Association, said Tuesday that there are no signs of faltering demand in Europe and the U.S. but warned that concerns over the economic outlook could affect consumer sentiment.

In August, Toyota said that its domestic production rose 12% from the same month a year earlier to 252,374 vehicles, with a growth in output for exports helping to offset the relatively high basis of comparison in the previous year. The company’s exports soared 19.8% to 137,977 vehicles.

Nissan said its domestic output declined 2.5% to 89,262 vehicles in August after three straight monthly rises, while Honda’s domestic output dropped 17% to 56,356 vehicles.

Suzuki said its production increased 5.9% to 86,215 vehicles, while Mazda posted a 5.6% rise to 68,449 vehicles.