Japan's nationalist Prime Minister Shinzo Abe has said the country's pacifist post-World War II constitution which limits its military to self-defence could be amended by 2020.

In a New Year comment published in the conservative daily Sankei Shimbun on Wednesday, Abe predicted the constitution "will have been revised" by 2020 when Tokyo hosts the Summer Olympics.

His comments come days after he enraged Asian neighbours and disappointed Washington by visiting a Tokyo shrine honouring the country's war dead, including World War II leaders, and been seen abroad as a symbol of Japan's militaristic past.

"(By 2020), I think Japan will have completely restored its status and been making great contributions to peace and stability in the region and the world," he said.

He added that Japan's elevated status could possibly help Asia become a "balanced and stable region".

Abe took power a year ago in an election landslide as Japan faced China's increasingly assertive military posture amid a fierce territorial dispute with Beijing over Tokyo-controlled islands.

He initially focused on improving the economy with stimulus packages, mixing big-spending and easy money policies.

In recent months, he has turned to his more conservative agenda, passing a state secrecy law which critics say is a threat to democracy in Japan.

In a New Year message, Abe reaffirmed his resolve to change the pacifist constitution imposed by the US after Japan's defeat.

"As it has been 68 years since its enactment now, national debate should be further deepened toward a revision (of the constitution) to grasp the changing times," he said.

"Now is the time for Japan to take a big step forward toward a new nation-building effort."

On his security policy, Abe said, "We will resolutely protect to the end Japan's territorial land, sea and air."

The premier has long agitated for the amendment of a key article in the constitution that limits its military to self-defence and bans the use of force in settling international disputes.

The country's well-funded and well-equipped military is referred to as the Self-Defence Forces (SDF).

Abe has said he would like to look into making the SDF a full-fledged military, a plan that sets alarm bells ringing in Asian countries subject to Japan's occupation in the first half of the 20th century.

In his first policy as premier last year, Abe said he would look to change a provision which requires a two-thirds majority in parliament to amend the basic law.

In his New Year message, Abe said the launch of a US-style National Security Council in December would help promote his "proactive pacifism" as a "'signboard of the 21st century' which should be borne by our country."