TOKYO, Jun. 12 (Reuters) - Chinese fighter jets flew unusually close to Japanese military patrol planes over the weekend, Tokyo said, after two Chinese aircraft carriers were spotted operating simultaneously in the Pacific for the first time.

Japan has protested about the incidents, Chief Cabinet Secretary Yoshimasa Hayashi said on Thursday.

"We have expressed serious concern to the Chinese side and solemnly requested prevention of recurrence," he said, referring to the June 7-8 incidents in which Tokyo said Chinese jets flew as close as 45 meters (148 feet) to Japanese planes.

On Saturday, a Chinese J-15 jet from the aircraft carrier Shandong chased a Japanese P-3C patrol aircraft for about 40 minutes, according to Japan's defence ministry.

On Sunday, a J-15 chased a P-3C for 80 minutes, crossing in front of the Japanese aircraft at a distance of only 900 meters (2,950 feet), it said.

The P-3C aircraft, belonging to Japan's Maritime Self-Defense Force based in the island of Okinawa, were conducting surveillance over international waters in the Pacific, the ministry said.

"Such abnormal approaches by Chinese military aircraft could potentially cause accidental collisions," the ministry said in a statement on Wednesday, attaching close-up images of the J-15 jet it took on Sunday. There was no damage to the Japanese planes and crew, it added.

Hayashi, the top Japanese government spokesperson, told a regular briefing that Tokyo will maintain communications with Beijing at various levels and ensure the monitoring of airspace around its territories.

Earlier this week, Tokyo said the Shandong and another Chinese carrier the Liaoning were conducting simultaneous operations in the Pacific for the first time, describing it as a move signifying Beijing's intention to further widen its capabilities beyond its borders.

Beijing has said the operations were a "routine training" exercise that did not target specific countries.

In 2014, Tokyo said it spotted Chinese military aircraft flying as close as 30 metres to its military aircraft over the East China Sea and protested to Beijing.

Photo from Reuters