Media playback is unsupported on your device Media caption BBC's Martin Patience: "Some of the protesters are pelting the embassy with plastic bottles and then they're moving on"

Fresh anti-Japan protests have erupted in China over disputed islands amid raised tension on the anniversary of Japan's invasion of north-east China.

Thousands of protesters chanted slogans outside the Japanese embassy in Beijing as riot police lined the streets.

Japan's coast guard says several Chinese ships are in waters near the islands, known as Senkaku in Japan and Diaoyu in China, Japanese media report.

This follows a brief landing by two Japanese activists earlier on Tuesday.

The islands have long been a point of contention and recent tension has led to fears of a naval conflict.

The latest developments fall on a politically sensitive anniversary, marking what is known as the ''Mukden incident''.

At the scene A sensitive date for China, 18 September marks the day in 1931 when Japan staged the excuse for its later invasion. This year's anniversary is particularly tense because of a mounting row between the countries over the disputed Senkaku/Diaoyu islands. In Beijing, thousands of protesters carrying banners and pictures of Mao marched in small groups past the Japanese embassy on Liangmaqiao Street. Despite the aggression of their chants, the protesters' mood was orderly. Hundreds of shirt-sleeved Beijing police kept guard. Protests in China are closely controlled, giving them an often choreographed air. The question now is whether, having let people vent their fury, China's authorities move to tone down the mood. Even if they did, none of the underlying tensions would have been addressed.

On 18 September 1931, Japanese soldiers blew up a railway in Manchuria, blaming it on dissidents. This was later revealed to be a pretext for the invasion of north-east China.

After meeting US Defence Secretary Leon Panetta, China's defence minister told reporters that Beijing hoped for a peaceful resolution to the dispute with Japan, Chinese state media reported.

"We reserve the right to take further actions, although we hope to settle the issue through peaceful negotiation," said Liang Guanglie.

Mr Panetta was in Beijing for talks with his counterpart and top Chinese leaders. He did not mention the dispute, but called for closer military contact between the US and China.

"Our goal is to have the United States and China establish the most important bilateral relationship in the world, and the key to that is to establish a strong military-to-military relationship," he said.

However, Mr Panetta, who was in Tokyo on Monday, had earlier warned of the potential for the conflict to escalate and urged both sides to show restraint.

'Law enforcement'

The fresh spate of protests across China on Tuesday follows days of protests from the weekend targeting Japanese businesses. Many of them, including electronic companies Panasonic and Canon, have suspended operations.

Japan-China disputed islands The archipelago consists of five islands and three reefs

Japan, China and Taiwan claim them; they are controlled by Japan and form part of Okinawa prefecture

The Japanese government signed a deal in September 2012 to purchase three islands from Japanese businessman Kunioki Kurihara, who used to rent them out to the Japanese state

The islands were the focus of a major diplomatic row between Japan and China in 2010 Q&A: China-Japan islands row

Two Japanese activists landed briefly on the disputed islands on Tuesday morning, reports said.

Last month saw a series of landings by both Chinese and Japanese activists on the islands.

A Chinese fisheries patrol boat was also spotted by the Japanese coast guard in waters near the islands, a Kyodo news agency report said.

Some 1,000 Chinese fishing boats are also headed for the area, Chinese media reported earlier.

The uninhabited but resource-rich islands are controlled by Japan and also claimed by Taiwan.

China maintains it has sovereignty over the islands in the East China Sea, saying that they have historically been part of China.

Last Friday, China sent six boats sent to "patrol" the islands after Japan sealed a deal to buy three of the islands from a private owner earlier in the week.

The China Marine Surveillance (CMS) will continue with the ''law enforcement activities'' to demonstrate China's jurisdiction over the islands, Chinese state media reported.

Analysts see Japan's decision to buy the islands as damage limitation in response to a much more provocative plan by the nationalistic governor of Tokyo, who wanted to purchase and develop them.

In Japan, the government seems unlikely to back down with an election looming.