The storm was moving toward the Okinawa island chain with gusts of to 198 kilometres per hour, the Japan Meteorological Agency said.
Television footage showed residents boarding up windows on the remote subtropical island of Minami-Daitojima near the main Okinawa island chain as strong gusts hit the area.
Officials urged local people to guard against the wind and possible landslides
Halong was expected to reach Japan's mainland by the weekend, about a month after Typhoon Neoguri killed several people and left a trail of destruction in the country's south.
Last weekend, a man drowned in a raging river while more than half a million people were advised to evacuate as heavy rain from Typhoon Nakri lashed Japan.