The Bank of Japan warned Thursday that risks to the global economy, including heightened trade tensions between the United States and China, are beginning to have an adverse effect on Japanese companies.

In a quarterly report on the nation's regional economies, the central bank said the impact of the ongoing trade war between the world's two largest economies has been limited so far but that "a gradually increasing number of firms are pointing to some effects, such as a decline in orders."

The BOJ, meanwhile, upgraded its assessment of two regions that have been recovering from a series of natural disasters last year: Hokkaido, which was hit by a magnitude 6.7 earthquake that caused an island-wide blackout in September, and the western Chugoku region, where flash floods killed more than 200 people in July.