SINGAPORE, Aug. 1 — Stock markets in Asia fell sharply today on concerns about widening mortgage woes in the United States and the threats they pose: that investors are being forced to sell Asian assets to cover losses in the United States, and that hard-pressed American homeowners will scale back their demand for Asian exports.

The Nikkei 225 stock average, the benchmark for the Japanese market, fell by more than 2 percent, erasing the gains it had made so far this year. Widely watched indexes in Hong Kong and Australia fell by more than 3 percent each. South Korea’s key index slid by 4 percent.

European stock markets followed the declines in Asia in their morning trading, and were generally down by 1 to 2 percent at midday there.

The FTSE 100 index in Britain was off 1.4 percent, the DAX in Germany dropped 0.9 percent and the CAC 40 in France slid nearly 1.8 percent.