Japan marks the 70th anniversary Tuesday of the end of the Battle of Okinawa, the bloodiest episode in the Pacific War, which killed 200,000 people.

Prime Minister Shinzo Abe is scheduled to speak at a ceremony in Itoman, at the southern tip of the island, near to the spot where terrified locals jumped from cliffs or were pushed to their deaths on the orders of Imperial soldiers taught never to surrender.

Thousands of visitors, many of them survivors of the war, filed to the black marble monument inscribed with the names of the fallen to pray and leave flowers early Tuesday morning, amid tight security.

More than 100,000 Okinawans and 80,000 Japanese troops died in the 82-day battle for the strategically placed island chain.

Over 12,000 American soldiers also perished in what many feared was a foretaste of the fight they would have to wage for the Japanese mainland.

That invasion never came, partly because of the atomic bombings of Hiroshima and Nagasaki, with a cowed Japan surrendering in August 1945. Okinawa was the only part of Japan in which battles were fought.

Entire families were wiped out, and almost everyone on the subtropical island lost at least one relative.

As well as those who committed suicide by plunging off cliffs rather than surrender, Americans found thousands more locals dead in the caves where they had been hiding to escape the furious US bombardment, which came by air, land and sea.

- High tension -

Yoshiko Shimabukuro, 87, one of over 200 schoolgirls mobilised as a battlefield nursing unit for the Imperial Army in March 1945, said she felt remorse for surviving the war when so many of her friends died.

"Especially in June, all sorts of memories come flooding back," she told AFP. "Memories, fear, sorrow, terror -- even after 70 years. I can't put into words the sadness and terror that comes flooding back.

"You accepted you could die at any time. I don't know how I survived, looking back."

The anniversary comes with feelings running high on Okinawa -- a one-time independent kingdom annexed by Japan in the 19th century and now the reluctant host to more than half of the 47,000 US troops still stationed in the country.

A controversial plan to move a US air base from a crowded urban area to a rural spot on the coast is proving deeply unpopular, with many wanting it to be put somewhere else altogether.

However, Tokyo and Washington have both insisted that the plan to move it -- conceived two decades ago -- is the only viable option for shuttering Futenma Air Station.

Renewed local opposition to the proposal and a series of angry protests have coincided with a push by Abe's nationalist government to give Japan's well-resourced, but tightly restricted, military more leeway to act internationally.

Critics say that runs counter to the country's pacifist constitution, which was imposed by US occupiers in the aftermath of WWII, but has since been adopted as an article of faith by large swathes of voters.