Japanese Prime Minister Yoshihide Suga has agreed with his Vietnamese counterpart to step up defence and security cooperation in the face of China’s expanding influence in the region.

In talks in Hanoi on Monday, Suga and Vietnamese Prime Minister Nguyen Xuan Phuc set a basic agreement allowing Japan to export defence equipment and technology to Vietnam.

Japan has been pursuing such agreements in recent years to bolster ties with Southeast Asia and provide a lifeline to its own defence industry.

Suga arrived in Hanoi late on Sunday on the first stop of a four-day visit to Vietnam and Indonesia that he says is key to pursuing the “free and open Indo-Pacific” vision for multilateral economic and security cooperation to counter China’s growing power and protect sea lanes in disputed areas of the South China Sea.

“Vietnam is crucial to achieving our vision of ‘the Free and Open Indo-Pacific,’ and our valuable partner,” Suga told a joint news conference after his hour-long meeting with Phuc.

Japan, as an Indo-Pacific nation, will continue to contribute to the peace and stability in this region.”

Suga said Vietnam was the most suitable destination for his first trip abroad as Japan’s leader.

Japan already has defence equipment transfer deals with the US, Britain, the Philippines and Malaysia, among other countries. Vietnam is a 12th partner.

Suga called the agreement “a major step” for a bilateral defence cooperation, saying he expects further developments.

Japan most recently exported a radar surveillance system to the Philippines in August.

In August, Vietnam agreed to buy six coast guard patrol boats worth $US345 million ($A487 million) from Japan to increase its maritime capacity.

That deal comes amid China’s continuing development and militarisation of artificial islands in the contested waters of the South China Sea.