Tokyo, Japan - Japan on Tuesday said that two massive Chinese aircraft carriers had been detected operating deep in the Pacific Ocean, in activities that have been flagged as first-of-their-kind.

On Monday, five Chinese vessels, including a missile destroyer, sailed inside Japanese economic waters around the remote ringed reef of Okinotori, Tokyo's defense ministry said.

The fleet included China's iconic Shandong and Liaoning aircraft carriers loaded with a vast assortment of fighter jets and helicopters. These vehicles proceeded to conduct take-off and landing exercises while in the Pacific.

The fleet of five warships had previously been detected sailing 340 miles southeast of Miyako Island, near Taiwan, on Saturday.

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"This is the first time two Chinese aircraft carriers were spotted operating in the Pacific at the same time," a Japanese defense ministry spokesperson said, per AFP.

"We believe the Chinese military's purpose is to improve its operational capability and ability to conduct operations in distant areas."

Japanese and US defense officials say that China's exercises indicate that it wants to push the US military out of the "first island chain," which stretches from Japan down through the Philippines.

Responding to Tokyo's accusations, Chinese foreign ministry spokesperson Lin Jian on Monday defended the operation and said that the activities were "fully consistent with international law and international practices."

"Let me reiterate that Chinese naval vessels’ activities in those waters are fully consistent with international law and international practices," Lin said on Tuesday when again asked by reporters

"Our national defense policy is defensive in nature. We hope Japan will view those activities objectively and rationally."