"As I promised in the election, my imminent task is to deal firmly with North Korea," he says.

It was a resounding victory for Japanese Prime Minister Shinzo Abe in a snap election on Sunday and he immediately vowed to "deal firmly" with threats from North Korea that dominated the campaign.

Mr. Abe's conservative coalition was on track to win 311 seats in the 465-seat Parliament, according to a projection from private broadcaster TBS, putting the nationalist Premier on course to become Japan's longest serving leader.

"As I promised in the election, my imminent task is to deal firmly with North Korea," Mr. Abe, 63, said. "For that, strong diplomacy is required," he stressed.

Mr. Abe was heading for a "landslide", the top selling Yomiuri daily said on its website.

But it was unclear in the immediate aftermath of the vote whether his coalition would retain its two-thirds "supermajority," requiring 310 seats, as some media had it falling just short.

A "supermajority" would allow Mr. Abe to propose changes to pacifist Japan's US-imposed constitution that forces it to renounce war and effectively limits its military to a self-defence role.

Mr. Abe said he would "deepen" debate on the divisive issue in Parliament but stressed: "I don't plan to propose [changes] via the ruling bloc alone. We'll make efforts to gain support from as many people as possible."