The support of Singapore, a key ASEAN country was announced by its Prime Minister Lee Hsien Loong who said the initiative will benefit development in the region.
The Maritime Silk Road (MSR) proposal was put forward by Xi to promote interconnection and create an economic belt, Lee told state-run China Daily ahead of his visit to China.
The project expected to dominate Xi's talks with leaders of the Maldives, Sri Lanka and India beginning on Sunday.
He would become the first Chinese President to visit the Maldives and the first to visit Sri Lanka in three decades.
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Xi will begin his first visit to India from September 17.
Besides MSR, which broadly aims to connect various Asian ports to improve trade and commerce for the revival of the ancient Silk Road connecting Central Asia and Europe is the main Chinese project being strongly promoted by Xi in all most all his trips abroad.
Xi has already invited the Maldives to be part of MSR when Maldivian President Abdulla Yameen visited China last month.
Yameen in a guarded response said the Maldives will respond to Xi's proposals, apparently keeping India's reservations in mind.
While India has conveyed its readiness to take part in BCIM during Vice President Hamid Ansari's recent visit, New Delhi has its own strategic concerns in its backyard in the Indian Ocean and has sought more details of the MSR plan.
As Xi is set to embark on his South Asia tour, the Hong Kong-based South China Morning Post said that China is expected to shore up its maritime strength by securing port development deals in Sri Lanka when President Xi Jinping tours Colombo which could spark concerns in India.
While Beijing is keen to make goodwill gestures to countries in the region, the port deals could stoke fears that China will use the facilities for strategic purposes, such as encircling India, a Post report said today.
The Hambantota port, on Sri Lanka's southern coast, is already heavily financed by Chinese loans, and is in the second phase of development.