Tokyo — An unused lifeboat, a door and other fragments believed to be from a Japanese army helicopter were found after the Black Hawk carrying 10 crew members was presumed to have crashed at sea, officials said Friday. Defense Minister Yasukazu Hamada, apparently struggling to hold back tears, told reporters that none of the missing crew members had been found as the search continued Friday.

He said he took the accident seriously and would take all precautious for the safe operations of Self Defense Force aircraft. “We will do our utmost for the rescue of the 10 people who are still missing, while continuing to gather information related to the extent of damage,” he said.

The UH-60JA Black Hawk helicopter disappeared Thursday afternoon while on a reconnaissance mission in Japan’s southern islands, according to the head of the Ground Self Defense Force, Yasunori Morishita.

It disappeared from radar only 10 minutes after departing from a base on Miyako Island and is believed to have crashed into the water between Miyako and nearby Irabu Island to the northwest. The area is about 1,120 miles southwest of Tokyo.

Coast guard patrol ships found an unused lifeboat whose serial number matched that of the missing helicopter and a door believed to belong to the same aircraft near the presumed crash site, army officials said.

The crash came as the country works to significantly bolster its defenses in response to China’s increasingly assertive military activity in the regional seas, where tension is also rising around Taiwan.

According to the Defense Ministry, Japan started deploying the Black Hawk, a twin-engine, four-bladed utility helicopter developed by U.S. manufacturer Sikorsky Aircraft and produced by the Mitsubishi Heavy Industry, in 1999 for rapid response, surveillance and disaster relief missions.

The helicopter was stationed at a key army base in Kumamoto prefecture on Japan’s southern main island of Kyushu, Morishita said Thursday night. One of its 10 crew members is the division commander, Yuichi Sakamoto, who was just promoted to the post at the end of March.

The army said the helicopter had a routine safety inspection in late March. No abnormality was found during its subsequent test flight or on its trip from its home base of Kumamoto to the Miyako island.

Black Hawks are flown by a number of militaries and other agencies around the world, and still used heavily by the U.S. Last month, the U.S. Army said nine soldiers were killed in a mid-air collision involving two Black Hawks near Fort Campbell, Kentucky, during a routine training mission.