The Coast Guard said it was searching for the yacht after its office in the southern Okinawa island received a radio distress signal earlier Sunday.

"We then confirmed it was a US-registered yacht, Jade Princess, with the US coast guard," the Japanese coast guard official said.

Four US citizens are aboard Jade Princess, which was sailing from Malaysia to Okinawa, the official said.

"We received the signal shortly before noon from a location some 83 kilometres (51 miles) south-southwest of Iriomote island," he said, referring to a small Japanese island near Taiwan.

The typhoon is the strongest to hit Taiwan this year. It is expected to reach Japan's Okinawa island chain by Wednesday, according to the Japanese Meteorological Agency.

Jangmi, meaning "rose" in Korean, made landfall in Taiwan's northeastern Ilan county around 0740 GMT Sunday, according to local officials.