A U.S. Navy F35C Lightning II combat jet conducting exercises in the South China Sea crashed while trying to land on the deck of an American aircraft carrier, injuring seven sailors, the military said.

The pilot ejected during the “landing mishap on deck” of the USS Carl Vinson on Monday. The pilot was recovered by a military helicopter and is in stable condition.

In total, seven sailors were injured, three who needed to be evacuated for medical treatment in Manila, Philippines, and four who were treated on board the ship. The three sent to Manila were reported in stable condition on Tuesday morning, the Navy said.

A U.S. Pacific Fleet spokesman said he had no more details on what caused the crash, which remains under investigation, or whether the multimillion-dollar aircraft could be recovered.

Two American carrier strike groups with more than 14,000 sailors and marines are conducting exercises in the South China Sea, which the military says is to demonstrate the “U.S. Indo-Pacific Command Joint Force's ability to deliver a powerful maritime force.”

As China has pressed territorial claims in the South China Sea and increased pressure on Taiwan, the U.S. and its allies have stepped up exercises in the region, in what they call freedom of navigation operations in line with international law.

As the Carl Vinson and Abraham Lincoln strike groups began their dual carrier operations on Sunday, China flew 39 warplanes toward Taiwan in its largest such sortie of the new year, according to Taiwan's defense ministry.

The formation of 24 Chinese J-16 and 10 J-10 fighter jets stayed out of Taiwanese air space, but the maneuver prompted Taiwan to scramble its own aircraft in response.

Chinese pilots have been flying toward Taiwan on a near-daily basis, and it was unclear if Sunday's flights were a response to the American exercises. China's Ministry of Foreign Affairs refused to comment.

Taiwan and China split during a civil war in 1949, but China claims the island as its own territory. Beijing has used diplomatic and military means to isolate and intimidate the self-ruled island, but the U.S. has continued to support Taiwan by selling it advanced weapons and fighter planes.