Recent moves by the Chinese Air Force show it has determined to expand its presence over oceans by conducting more long-distance drills and developing new bomber aircraft with longer ranges, according to military officers and experts.

The latest move came on Thursday, when six People's Liberation Army Air Force H-6K bombers flew through the Miyako Strait between the islands of Okinawa and Miyako in the East China Sea and approached the Kii Peninsula, Japanese media quoted the Japanese Defense Ministry as saying. This was the first time the PLA Air Force flew along that route, the report said.

The Air Force also disclosed the operation on its micro blog, saying that Chinese military aircraft would make more such training runs in the area. The account published a photo of an H-6K taken by the crew of another bomber during the mission.

"Such regular, long-distance exercises are in line with international laws and international practices. They are the normal needs of the PLA to enhance our combat capability and build a strong air force," said Senior Colonel Shen Jinke, an Air Force spokesman.

The H-6K is the PLA's most advanced bomber and is capable of carrying supersonic cruise missiles for strikes against land or sea targets.

General Ma Xiaotian, the PLA Air Force's commander, said earlier this month in Changchun, Jilin province, that the Air Force "must carry out drills at sea".

"Our Air Force cannot simply guard on land and not fly out", he said in response to questions on Japan's concerns about the PLA's "increasing activities" over the Sea of Japan.

Ma said it is normal for the Chinese Air Force to conduct training and exercises over the Sea of Japan and that "the Sea of Japan is not Japan's sea".

The PLA Air Force started to perform long-range, ocean-bound drills in March 2015. At first, the frequency was about four times a year, but now it is several times a week. In July, the PLA Air Force carried out exercises over the Bashi Channel and Miyako Strait with several types of aircraft, according to Shen.

Colonel Ren Guoqiang, a Defense Ministry spokesman, said in July that other nations should not "make a fuss about or over-interpret" the Chinese military's oceangoing exercises.

Wang Ya'nan, editor of Aerospace Knowledge magazine, said these long-range drills would enable the Air Force and the PLA Navy's aviation units to push China's defense line farther into the ocean and to better safeguard the country's maritime routes.

In addition to intensified training, the Air Force also has commissioned Aviation Industry Corp of China, the leading Chinese aircraft producer, to develop a new-generation of long-range strategic bombers capable of fulfilling intercontinental missions, Air Force sources said.

Photos circulating on Chinese online forums indicate that the Air Force also is testing a variant of the H-6K equipped with a refueling probe, which enables the new model to be refueled in flight and thus operate farther than existing models.