Japan's prime minister won Dhaka's support for Tokyo's bid for a non-permanent seat on the UN Security Council as he began a visit to Bangladesh and Sri Lanka aimed at offsetting China's mounting influence in South Asia.

Bangladeshi Prime Minister Sheikh Hasina said Dhaka would withdraw its candidacy in favour of Tokyo in view of Japan's "continued and strong support in Bangladesh's development process".

Hasina's announcement came after her official summit with Japanese Prime Minister Shinzo Abe, who is on a three-day visit to the region to boost economic and security ties.

Dhaka has been campaigning for a Security Council seat for years, but local officials said Japan's commitment to invest in some of the country's key infrastructure projects changed its decision.

Abe is the first Japanese premier to visit Bangladesh in 14 years. On Sunday, he will leave for Sri Lanka on the first trip by a Japanese prime minister in 24 years, where he will meet President Mahinda Rajapakse.

His South Asia tour follows Indian Prime Minister Narendra Modi's trip to Tokyo earlier in the week during which the two countries, which both have prickly relations with giant neighbour China, declared they would raise ties to a "new level".

Speaking to reporters before leaving Tokyo, Abe called Bangladesh and Sri Lanka "countries with a growing influence in economic and political domains".

In Dhaka, Abe and Hasina signed a joint statement, in which Japan reiterated its support for some of Bangladesh's major infrastructure projects. Dhaka said it would set up an industrial park exclusively for Japanese investors.

- 'Milestone' in relations -

Bangladesh has described Abe's tour as a "milestone" in relations and hoped to win Japanese investment for infrastructure projects including a railway bridge and a tunnel under the Brahmaputra river.

Abe, who is accompanied by dozens of top corporate executives, told a forum of Japanese and Bangladeshi businessmen that ties between the two nations have entered a "new level" and both were "going to help each other like sister and brother".

Abe has said Tokyo would support Dhaka's Bay of Bengal Industrial Growth Belt initiative to spur economic growth in the impoverished nation, but called for "further improvement of investment environment" in the country.

"I express my commitment once again that Japan will extend economic cooperation amounting to about $6 billion for roughly four to five years including about $1.2 billion... which has already been provided," Abe said.

He added that Tokyo was "deeply grateful" for Bangladesh's decision to support its UNSC candidature.

Bangladesh's premier visited Japan in May when Tokyo announced the $6 billion in aid for Dhaka. The deal was a boost to Hasina, coming months after she won a disputed election marred by widespread fraud and an opposition boycott.

Dhaka last month announced Japan would lend about $4 billion for an ambitious coal-fired power-plant project, which includes a deep-sea terminal. Japan is already Bangladesh's largest bilateral donor and is a fast-growing export destination.

Japan's state aid agency has shown interest in building a deep-sea port in Bangladesh's south for which Dhaka earlier approached China.

Bangladesh and Sri Lanka lie along sea-lanes between the Middle East and East Asia. China has helped build ports in countries along the vital route.

In Colombo, Abe and Rajapakse aim to strengthen maritime territorial cooperation in the face of a more territorially assertive China, media reports said.

Japan is ready to provide patrol boats to help Sri Lanka bolster its maritime guard, according to the reports.