Thousands gather in sweltering heat on the southern Japanese island of Okinawa to protest against a U.S. marine base positioned there.

Days ahead of a visit by U.S. President Barack Obama, demonstrators demanded the base be moved out of the region.

The row over the re-siting of the Futenma air base threatens to stall a reorganisation of the 47,000 military personnel in Japan.

It could also sour defense ties between the U.S. and Japan.

The two countries' alignment is seen as key in a region where China is rising in power and North Korea remains unpredictable.

But the thousands of demonstrators want the existing base gone and plans for a replacement built on reclaimed land scrapped.

[Unidentified Japanese Protester]:
"The idea of building another base on this tiny island — and even by reclaiming the sea — is just insane."

Okinawa makes up only 0.6 per cent of Japan's land mass, but hosts half the U.S. troops in Japan.

Those living near the base complain of noise, crime, pollution and accidents.