"Generally speaking, it is important that the overseas export of Japan's agricultural, forestry, and fishery products and foodstuffs is smooth," chief government spokesman Minoru Kihara said when asked about the reports.

"Generally speaking, I believe that international trade in rare earths should proceed smoothly, and I consider this to be extremely important," Kihara told a regular briefing.

Kyodo News reported that China-bound exports of Japanese sake and food items have been delayed, citing trade industry sources.

The "slow customs clearance" is believed to be part of China's reaction to Prime Minister Sanae Takaichi's suggestion in November of a Japanese military response to any seizure of Taiwan by Beijing, Kyodo said.

The Japanese embassy in Beijing has received enquiries from affected companies, according to Kyodo.

The mission has urged China to properly handle trade procedures and ensure transparency, the news agency reported a source familiar with bilateral relations as saying.

Separately the Wall Street Journal reported that China has begun choking off exports of rare earths and rare-earth magnets to Japan.

On Tuesday, China announced a broad ban on the export to Japan of "dual-use" goods with potential military applications.

China has since begun restricting exports to Japanese companies of scarce and expensive "heavy" rare earths, as well as the powerful magnets containing them, the Journal said, citing two exporters in China.