China’s top military commander on Friday bought five new warships, a jet fighter and other military equipment, as part of efforts to expand its capabilities, state media reported.

The move comes amid a worsening dispute with Japan over the islands, and comes as Beijing is increasingly worried about Japan’s assertiveness in the region.

The latest acquisitions were all part of China’s “national defense expansion,” the state-run Global Times newspaper said.

The purchases were made through an online auction site, and included the aircraft carrier Zhengzhou-class, the navy’s newest aircraft carrier, and the amphibious assault ship Zumiez, which is also under construction.

The Chinese navy has been steadily expanding its military capacity in recent years as China and its neighbors seek to contain its ambitions to dominate the Pacific and the South China Sea.

In a bid to reassure neighbors that China was serious about defending its territorial claims in the South and East China Seas, the Chinese navy on Wednesday launched a joint patrol with the Philippines to counter Japan’s claims in a disputed region.