A volcanic island off Japan's southern coast continues to smoulder with lava flowing from its craters into the sea, new aerial images showed Friday.

Nishinoshima, some 1,000 kilometres (620 miles) south of Tokyo, joined up with a small volcanic islet formed in November and the new mass now measures 1.26 square kilometres (0.49 square miles) around, the Japanese coastguard said.

The agency's images showed a few craters on Nishinoshima spewing columns of smoke 1,500-2,000 metres (4,900-6,600 feet ) high as molten lava flowed into the sea, sending clouds of white steam into the sky.

Nishinoshima is estimated to be 10 million years old.