Thailand’s environmental policy and planning body approved the impact assessment of the project’s first phase on November 30, according to its website.

That means construction of the first phase – a 250km railway running from Bangkok to the northeastern province of Nakhon Ratchasima – can begin. It was due to start in November.

Thailand in July approved US$5.2 billion in funding to build the first phase but the project has been stalled over issues including cost, development rights and labour problems.

On Sunday, Muangkeo said the project was “not feasible” for Thailand given its high construction cost and low potential for use.

“We will talk to China to have a clear answer first [as to whether the railway should be used] to carry goods or carry passengers,” Muangkeo said, adding that this was a matter that still needed to be resolved.

Under the deal, Thailand will own the project and be responsible for financing its construction, while China will design it and provide engineers, track systems and equipment.

“The costs are in the billions of dollars, so we have to have at least 9 to 10 million passengers a year – compared with the population of 60 to 70 million in Thailand,” Muangkeo said.

“I would like to have China express clearly [what the railway will be used for]. Goods transport is feasible,” he said, adding that Beijing should also be clear about the use of other transport projects it is involved in across the region.

The first phase is part of a bigger railway development that will stretch more than 1,260km, from Bangkok to southern China. It will be Thailand’s first high-speed railway and is one of a number of high-profile projects being developed as part of China’s ambition for a pan-Asia railway network spanning from Kunming in Yunnan province through Laos, Thailand and Malaysia to Singapore. Construction of the Laos section began last year.

While concerns have been raised about China’s rising economic and geopolitical influence in the region, Muangkeo said Thailand’s main worry was whether the project was feasible.

“Costs and profits [have to be] balanced,” he said.

He added that China should take more responsibility to control the cost of projects such as the railway that are part of its “Belt and Road Initiative” to grow global trade.

“I would like to request that China consider and find the best solution – including ... to minimise the costs and maximise the profits for all the countries on this path,” Muangkeo said.

“Most of the investment, construction, funding, technology and labour comes from China ... We need to see [that a project] is really feasible before we start.”

Xue Li, a researcher with the Chinese Academy of Social Sciences, said the issue of whether to use the railway for passengers or freight had been the subject of debate in Thailand.

“But since the railway will go through areas with fewer people, it is likely there would be greater demand for trains to carry freight,” Xue said. “The Chinese side is fine with either option.”

Hu Zhiyong, a research fellow with the Institute of International Relations at the Shanghai Academy of Social Sciences, said it was up to both Thailand and China to make the decision.

“Given Thailand’s population density ... building a railway will help passengers by saving them time and improving efficiency,” Hu said. “Thailand has a great need for high-speed railway services.”

Additional reporting by Sarah Zheng