Chinese premier Li Keqiang is set Friday to sign agriculture and transport agreements on a visit to Bangkok, as Thailand's junta seeks diplomatic support after their coup was given short-shrift by US and European allies.

A dual-track railway through Thailand, part of a 1,400 kilometre (870 mile) vision of linking China's southwestern hub city of Kunming with Asia's second busiest port of Singapore, will be the centrepiece of Li's visit, a Thai government spokesman told AFP.

Li will sign a Memorandum of Understanding with Thai counterpart Prayut Chan-O-Cha, that will pave the way for a joint-venture to build two railways lines through Thailand.

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

"The railways are a very important issue," Yongyuth Mayalarp told AFP.

"This is fundamental and will reinforce our cooperation with China."

Construction on the lines will start next year and be completed by 2022, he added, without giving a projected cost for the ambitious infrastructure link.

Further MoUs on rubber and rice will also be inked, he added.

Li joins regional leaders -- including from Myanmar, Cambodia and Laos -- for the Greater Mekong Summit in Bangkok, where mega-dams and hydro-electric power schemes will also be up for discussion, despite mounting concerns over the environmental and social impact.

But Li's visit will also be widely interpreted as an endorsement of Thailand's new military rulers, who grabbed power from the elected government in May.

Since the coup, Thailand has found itself out of favour with Western allies, including the US and European Union who have repeatedly called for a swift return to democracy.

The junta is desperate to project an image of business as usual, although the Thai economy remains weak after months of anti-government protests hobbled the previous administration, paving the way for the army putsch.

The meeting with Li will show "the good relationship we have with China" Yongyuth said, while the presence of the other regional leaders, "reflects the fact that situation is normal now in our country."

"They (the leaders) are all confident in the situation in Thailand and in the way the country is running," he added.

China has in recent months devoted diplomatic energy, as well as huge sums of money, to wooing Southeast Asia, 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 Beijing is determined to outmanouevre 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.