The surplus in the current account, the broadest measure of Japan's trade with the rest of the world, stood at 503.6 billion yen ($6.3 billion) in September, the finance ministry said.

The figure was smaller than expected by economists surveyed by the Nikkei economic daily and Dow Jones Newswires, who estimated a surplus of 762.3 billion yen.

Thursday's data are the latest to show that export weakness remains a risk to the world's third-largest economy as a slowdown in the global economy, a strong yen and a territorial spat with China weighs on demand for Japanese products overseas, analysts said.

The current account measures trade in goods, services, tourism and overseas income.

The trade deficit in September stood at 471.3 billion yen, compared with a surplus of 372.3 billion yen a year earlier as EU- and China-bound exports declined while imports of crude oil increased, the finance ministry said.

The income surplus, or returns on overseas investment, shrank by 6.0 percent from a year earlier to 1.31 trillion yen, it said.

"Today's outcome is more evidence that Japan's trade conditions are bad," Mizuho Securities Research and Consulting senior economist Norio Miyagawa told Dow Jones Newswires.

Imports are rising "as buying of natural resources became active again," he said, adding that exports to China may decline further ahead "as we will likely see a more full-fledged impact from the Japan-China territorial dispute."

Tokyo and Beijing have been embroiled in an increasingly bitter row over an East China Sea archipelago, called the Senkakus in Japan and the Diaoyus in China, which Japan nationalised in September.

The spat has led to thousands of flights being cancelled between the nations, while Japan's top three automakers said their sales in China have plunged.