The Chinese-backed Funan Techo canal has sparked fears in neighbouring Vietnam that it could be used by Chinese warships, and reduce Cambodian dependence on Vietnamese ports.

Environmentalists are also concerned that the 180km canal will potentially reduce water flow to the Mekong, among the world’s most biodiverse rivers.

Cambodia received billions from China in infrastructure investments as one of Beijing’s closest regional allies under former leader Hun Sen.

Hun Manet, his son, said the Funan Techo canal would mostly be funded by Cambodians and that the government is in talks with a Chinese company for further investment.

“We will do it now, we can’t wait for anybody any longer,” Hun Manet said in a speech today.

Opposition figurehead Sam Rainsy, who lives in exile, has alleged that the project would serve the interest of China.

The waterway is part of Beijing’s huge Belt and Road Initiative, a massive infrastructure scheme across Asia, but Hun Manet insisted it will only serve Cambodia.

“(We) do it within the Cambodian territory for the Cambodian people and for the interest of Cambodia,” he said.

“We will have a groundbreaking ceremony this August.”

The canal – 100m wide and 5.4m deep – will connect Phnom Penh with Cambodian ports on the Gulf of Thailand.

Cambodia and China also wrapped up their largest annual military exercises today, involving several Chinese warships and hundreds of Chinese military personnel.

In December, two Chinese warships made a first visit to a Cambodian naval base that the US says could be used to boost China’s influence in the Gulf of Thailand.

Cambodian officials have repeatedly denied that the base, near the port city of Sihanoukville, is for use by any foreign power.

US defence secretary Lloyd Austin is set to visit Cambodia on Tuesday.