TOKYO: Prime Minister Shinzo Abe called on new graduates of Japan's National Defence Academy Sunday to guard the country against "provocations" as tensions simmer with China over the sovereignty of an island chain.

In a dramatic speech, he emphasised that the security situation had changed since the students started their course four years ago.

"Unlike four years ago... provocations are continuing against our country's territorial land, sea and air," Abe told the graduation ceremony at the school in Yokosuka outside Tokyo.

"What is happening in the field where you will be is a harsh reality and a crisis that is there," he added.

"I wish you to dedicate yourselves to noble duty in the field, to defend the people and the country."

Drawing a vivid picture of their mission, Abe said: "The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood."

The line was a direct quote from a speech made by US President Theodore Roosevelt in 1910 in Paris.

Abe made the speech as China continued sending state-owned ships close to the disputed Tokyo-controlled Senkaku islands, which Beijing also claims and calls the Diaoyus.

Three marine surveillance ships from China were spotted Sunday morning about 40 kilometres (25 miles) off Kubajima, one of the islands in the East China Sea.

Chinese ships have routinely circled the islands since September when Tokyo nationalised some of the chain. They have sporadically entered 12-nautical-mile territorial waters around the islands.

Abe's Liberal-Democratic Party pledged at an annual convention Sunday to accelerate efforts to reform Japan's pacifist post-war constitution to emphasise the country's rights to defences and create a fuller military.

As part of the speech to graduates, Abe -- a hawk who took power for a second time in December when his conservative party scored an election landslide --

noted that his government had approved a rise in defence spending for the first time in 11 years.

"We will aim to upgrade the ability of the Self-Defence Forces in such regions as the southwest region (Okinawa)," he said. Japan considers the Senkakus as a part of Okinawa.

"Our country must play a greater role in enhancing the deterrent power of the Japan-US security arrangements," he added.

Most of the academy's 424 new graduates attended the ceremony, including 27 women and 11 foreign students from Cambodia, Indonesia, Mongolia, Thailand and Vietnam.