Japan on Friday announced it would give the Philippines two new vessels to boost Manila's capacity to patrol its waters, with the allies facing Chinese aggression in separate maritime disputes.

Japan, the Philippines' top source of aid, said it was also discussing with Manila the lease of surveillance aircraft to help its under-equipped coast guard.

The new vessels and planes are on top of 10 coast guard ships that Tokyo pledged to the previous Philippine leader Benigno Aquino.

Japan and China are locked in a long-running dispute over uninhabited islets in the East China Sea, while Manila and Beijing have overlapping claims in the South China Sea.

"We are talking about big-sized, 90-metre (295-foot) long vessels. We are also discussing the possibility of leasing aircraft designed for training. They are surveillance aircraft," Masato Ohtaka, deputy press secretary for Japan's foreign ministry, told reporters in Manila.

A UN-backed tribunal last month rejected Beijing's claims to most of the South China Sea which reach close to the coasts of the Philippines and other Southeast Asian nations.

Ohtaka said the new ships were among topics discussed by Japanese Foreign Minister Fumio Kishida and President Rodrigo Duterte on Thursday in the southern Philippine city of Davao.

Duterte said Thursday night he told Kishida about his "soft landing" approach to dealing with China following the tribunal's decision.

"(I don't want) to start hostilities at this time of our lives and he said Japan would do the same. They just want dialogue. They do not want further incursions," Duterte said.

Philippine foreign secretary Perfecto Yasay said Thursday Manila and Tokyo shared the same experience of dealing with Beijing's "intimidation" at sea.

He and Kishida urged Beijing to observe the rule of law after China vowed to ignore the ruling.

Beijing has conducted massive reclamation in the South China Sea, with a US-based think tank releasing images this week showing what appears to be China building military aircraft hangars on disputed reefs.

Ohtaka said Duterte and Kishida also discussed Japan's $2.4 billion loan for a new railway aimed at easing Manila's notorious gridlock.

The 38-kilometre (24-mile) elevated commuter line would connect Manila to nearby Bulacan province to decongest the capital and help spur economic activity.

"This is one of the biggest projects Japan has ever embarked upon using the yen loan," said Ohtaka.

Ohtaka added Japan was also open to building a railway in the southern region of Mindanao, a project Duterte previously said China had offered to fund.

Duterte has said reducing traffic congestion and fixing the deteriorating transport system are priorities for his administration.

Manila's traffic problems cost the Philippines an estimated $64 million a day in 2015, a Japanese-funded study found.