North Korea fired two short-range rockets off its east coast Wednesday, South Korea said, the latest in a series of missile tests ahead of a state visit to Seoul by Chinese President Xi Jinping.

A spokesman for the defence ministry in Seoul said the test appeared to be of two "multiple-launch rockets" with a range of around 180 kilometres.

It marks the third such test by the North in the past week -- all three involving firing into the Sea of Japan (East Sea).

Japan, which is currently engaged in talks with North Korea on the abduction of Japanese citizens during the Cold War, has officially protested the tests, calling them "extremely regrettable".

The latest launches come on the eve of Xi's arrival in Seoul for a two-day state visit and a summit with South Korean President Park Geun-Hye, which has been seen as something of a snub to Pyongyang.

As North Korea's chief ally and economic benefactor, China is widely seen as the member of the international community with the most leverage over the regime in Pyongyang.

Seoul and Washington have persistently called on Beijing to exert more pressure on the North to abandon its nuclear weapons programme.

It will be Park's second summit with Xi, who has notably not yet met with North Korean leader Kim Jong-Un since Kim came to power following the death of his father, Kim Jong-Il, in December 2011.