Construction on a $12 billion Chinese-backed railway through Thailand will begin in September, officials said Thursday, as part of a grand vision to overhaul the country's notoriously creaking network.

"The first two phases will start by September or October at the latest this year and will take around two-and-a-half years to complete," Thailand's Transport Minister Prajin Juntong told reporters after meeting Chinese officials in Bangkok.

Thailand currently has only 250 kilometres (155 miles) of dual track railway, making train travel painfully slow.

With Chinese help, Bangkok plans to lay down two new dual track lines, part of a wider regional network that Beijing hopes will eventually link China's southwestern hub city of Kunming with Asia's second busiest port of Singapore.

The largest line will cut 734 kilometres through Thailand, from northern Nong Khai province -- which borders Laos -- to the vast, coastal industrial estate of Map Ta Phut, southeast of Bangkok.

Prajin, the former head of Thailand's airforce, said construction on that line would be divided up into four stages with the first beginning in September, laying down tracks between Map Ta Phut and Kaeng Khoi, via the capital.

In total the four stages are expected to cost around 400 billion baht ($12 billion), the Ministry of Transport said in a statement.

Completion of all stages is expected by around 2020 with further meetings to be held in Beijing in February to decide the level of Chinese involvement.

Thailand's generals, who took over in May, are desperate to project an image of business-as-usual after their coup was strongly criticised by Western allies.

The Thai economy remains weak after months of anti-government protests hobbled the previous administration, and the US and European Union have repeatedly called for a swift return to democracy.

But Bangkok's relationship with Beijing has blossomed.

"This is a new era in Thailand and China's relationship," Deputy Foreign Minister Don Pramudwinai told reporters at a press conference Thursday.

Last month Chinese premier Li Keqiang and Thai junta leader Prayut Chan-O-Cha, who is also prime minister, signed an agreement over the railway's construction in a visit widely interpreted as an endorsement by Beijing of Thailand's new military rulers.

China has in recent months devoted diplomatic energy, as well as huge sums of money, to wooing some Southeast Asian nations, where its reputation as a regional powerhouse is blighted by sea disputes and fears over its long-term intentions.

In November Beijing pledged $20 billion in soft loans and for infrastructure projects to the 10-members of the Association of Southeast Asian Nations during a summit in Myanmar.

Experts say it is determined to outmanoeuvre the US, which has embarked on a security "pivot" towards Asia, as well bolster its trade routes and access to resources as China's breakneck development continues.