Image copyright Reuters Image caption One of the two planes involved in the incident was a KC-130 refuelling tanker (like the one seen in this archive picture)

A big search and rescue operation is continuing in Japan for five missing US Marines after two aircraft with seven crew collided and crashed into the sea.

One Marine was rescued and was "in fair condition", while another one "has been declared deceased", Marines officials said in a statement.

The planes involved were a KC-130 and an F/A-18 based at Iwakuni near Hiroshima, south-western Japan.

US media say they crashed during a mid-air refuelling exercise.

The Marine Corps has not officially confirmed this, describing the incident as a "mishap".

How is the rescue going?

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

The US 7th Fleet is supporting the operation, with navy aircraft being deployed.

Image copyright Reuters Image caption US aircraft and Japanese vessels are searching the area

A Marines statement said: "We are thankful for the Japan Maritime Self-Defence Force's efforts as they immediately responded in the search and rescue operation."

The Marines Corps tweeted that the incident occurred at about 02:00 local time on Thursday (17:00 GMT Wednesday).

The first Marine was rescued about four hours later, Japanese officials said, while the second was found 10 hours after the collision.

They said one of them was from the fighter jet.

There were five personnel on the C-130 and two on the F-18.

Japan said the search operation would continue overnight, Japan's NHK World reports.

It quoted the head of Japan's Self-Defence Forces, Katsutoshi Kawano, as saying that search teams had spotted debris floating in the sea.

How did the events unfold?

A Facebook posting by the III Marine Expeditionary Force said the incident took place 200 miles (320km) off the coast.

The US planes had taken off from Marine Corps Air Station Iwakuni and "were conducting regularly scheduled training when the mishap occurred".

Image copyright AFP Image caption An F/A 18E Super Hornet on the USS Ronald Reagan. It is not yet known which variant was involved in the incident

The BBC's Rupert Wingfield-Hayes in Tokyo says that air-to-air refuelling is a difficult and potentially dangerous flight operation, especially when done at night.

He says it is not clear what the weather conditions were like but overnight there was widespread cloud and rain across the Japanese archipelago.

The KC-130 is an extended-range tanker version of the C-130 and is used for mid-air refuelling.

The McDonnell Douglas F/A-18 Hornet is a fighter and attack aircraft and can carry a wide range of missiles and bombs.

The US has more than 50,000 troops stationed in Japan, more than 18,000 of them in the US Marine Corps.

The US has had problems with reliability of its aircraft in Japan. In November an F/A-18 Hornet crashed into the sea south of Okinawa. The two pilots ejected and were rescued.

Last December, part of a US helicopter crashed on to a school in Okinawa, renewing tensions with the local population.

Over the past years, a number of accidents and crimes have led to growing local opposition to the US base there.