An American military helicopter made an emergency landing in Okinawa on Monday, just two days after a similar incident on the southern Japanese island.
It was the latest in a series of accidents involving US military equipment that have fuelled local opposition to the basing of American forces on the island.
There were no immediate reports of injuries or damage after the helicopter landed near a hotel in the village of Yomitan, an Okinawa police spokesman said.
“We do not know about the cause as the incident is still under investigation,” the spokesman told AFP.
The US military could not immediately be reached for comment.
On Saturday, another US military helicopter made an emergency landing on a beach in Okinawa but no one was injured.
A faulty rotor may have caused the incident, a Japanese official said after talking with the US Marine Corps.
Last month, a window from a US military helicopter fell onto a school sports ground near the Futenma marine air base in Okinawa, but again no one was injured.
In October an American military helicopter burst into flames after landing in an empty field on the island.
Such accidents have sparked opposition to the US bases on the strategic island, which would serve as a launchpad for any American military activity in Asia.
A series of crimes including rapes, assaults, hit-and-run and drink-driving accidents by US personnel have also triggered protests on Okinawa, and are a frequent irritant in relations between close security allies Japan and the United States.
More than half the 47,000 American troops in Japan are stationed on Okinawa, the site of a major World War II battle that was followed by a 27-year US occupation of the island.