TOKYO, Japan - The U.S. Marine Corps and the Japanese Defence Forces launched a massive search and rescue operation off the coast of Japan after two U.S. Marine planes collided mid-air on Thursday morning.

According to U.S. officials, a Marine refuelling plane and a fighter jet crashed into the Pacific Ocean off Japan's southwestern coast after colliding mid-air early on Thursday morning. 

In a statement, the U.S. Marine Corps said that an F/A-18 fighter jet and a KC-130 refuelling aircraft were involved in a crash that took place at 2 am, during regular refuelling training. 

Marines officials said that the two planes collided after taking off from their base in western Japan's Iwakuni.

The III Marine Expeditionary Force released a statement on Facebook and said that the incident took place 200 miles (320 km) off the coast. 

It said the U.S. planes had been "conducting regularly scheduled training when the mishap occurred," with reports later adding that the planes crashed during a mid-air refuelling exercise.

Further, Japanese officials too released a statement saying the crash occurred about 60 miles (100 kms) from the coast.

Authorities said that the planes were together carrying seven crew members, with two travelling aboard the F/A-18 and five others in the KC-130.

Subsequently, a massive search and rescue mission was launched in the sea south of the Muroto Cape on Shikoku Island in southwestern Japan - which was the area of the crash.

The Maritime Self-Defense Force said that it had dispatched aircraft and vessels to join in the search operation.

Meanwhile, the Japanese Defence Minister Takeshi Iwaya said that Japanese aircraft and three vessels were taking part in the rescue operation.

The rescue operation has also received support from the U.S. 7th Fleet, that has deployed navy aircraft.

Later, the Maritime Self-Defense Force confirmed that two crew members have been found, while five still remain missing.

The two rescued crew members were rushed to a hospital on the base in Iwakuni. 

Japanese rescuers told the local media that one of the crew members rescued from the fighter jet was in a stable condition. 

Marines officials later said that the second crew member "has been declared deceased."

So far, authorities have not commented on the cause of the crash, claiming that an investigation is ongoing. 

Following the incident on Thursday, the U.S. President Donald Trump took to Twitter and offered thoughts and prayers to the crew members.

Trump also thanked Japan for their "immediate response and rescue efforts."

He wrote, "My thoughts and prayers are with the @USMC crew members who were involved in a mid-air collision off the coast of Japan. Thank you to @USForcesJapan for their immediate response and rescue efforts. Whatever you need, we are here for you. @IIIMEF"

The most recent incident in what has been a series of accidents involving the U.S. military forces deployed in and around Japan over the last few years occurred last month.

A U.S. Navy F/A-18 Hornet from the aircraft carrier USS Ronald Reagan crashed into the sea southwest of Japan's Okinawa Island.

Both the pilots aboard the Hornet were rescued safely.

Before that, in mid-October, a MH-60 Seahawk crashed off the Philippine Sea shortly after takeoff.

Over a dozen sailors suffered injuries in the incident.