Thailand may have to reevaluate its "strategic" relationship with China given the superpower's rise, an academic at one of Thailand's leading universities warned on Monday.
"We can't just look at [our invitation to the ongoing] Brics Summit. We have to look at what China has done. It has shown it was ready to use tough measures against Thailand," said Prapat Thepchatree, director of Asean Studies at Thammasat University.
Thai authorities claim Beijing's decision to invite Prime Minister Prayut Chan-o-cha to the summit reflects the nation's importance as an advanced market in Southeast Asia in the eyes of the Asian superpower. But critics suspect this is no longer the case.
"We can't just fall back on the old way of thinking that says Thailand and China have a fraternal bond," Prof Prapat said.
"When China first opened up [to the international community] it only had ties with a few countries including Thailand. But now China is immensely powerful."
China is hosting the three-day conference, which ends on Tuesday, in the port city of Xiamen in southern Fujian province.
Leaders have called for greater anti-protectionism, cautioned against provoking North Korea over its nuclear tests, and rallied for the grouping of member states Brazil, Russia, India, China and South Africa to claim a bigger say in global affairs.
Thailand was invited by Chinese President Xi Jinping along with four other nations including Egypt and Mexico as China has proposed building a so-called Brics Plus including "friendly" developing countries.
Two cooperation contracts for the Sino-Thai high-speed train project have already been signed during the summit as Gen Prayut and Mr Xi held a bilateral meeting.
However, Gen Prayut was not among the 30 leaders invited to the Beijing-hosted Belt and Road Forum in May to discuss greater connectivity from Asia to Europe and beyond, Prof Prapat said.
The Minister of Digital Economy and Society as invited instead along with four other ministers.
The Foreign Ministry explained his exclusion by rationalising that Gen Prayut had already agreed to attend the Brics Summit.
Prof Prapat cited rumours that the real reason may have been due to Thailand prevaricating on whether to agree to the Thai-Sino rail project.
Later in June the premier exercised his sweeping powers under Section 44 of the charter to fast-track the deal.
One of the contracts signed on Monday concerns the design of the rail project from Bangkok to Nakhon Ratchasima while the other relates to how the scheme will be supervised. The contracts for the 253-kilometre project are worth 5.2 billion baht.
The two leaders inked two more deals covering the Joint Plan of Action on Thailand-China Strategic Cooperation and a Memorandum of Understanding on Cooperation within the Framework of Silk Road Economic Belt and the 21st Century Maritime Silk Road initiative.
Despite the apparent snub, Pisanu Rienmahasarn, a former deputy permanent secretary for commerce, insisted Thailand is still China's most important partner in Asean.
China sees it as a core pillar coordinating with other members in the bloc, said Mr Pisanu, who now serves as senior director of the China-Asean Studies Centre at the Panyapiwat Institute of Management.
Prof Prapat said Thailand should use the meeting to flash its close ties with China to the world.
During the bilateral talks, Gen Prayut reiterated the regime's commitment to fostering a closer strategic partnership.
Thailand also supports China's One Belt, One Road initiative and is ready to promote greater connectivity between the two nations, the premier said.
The initiative conforms to the Eastern Economic Corridor policy, he added.
Support for the 2030 agenda for sustainable development and South-South cooperation were also expected to be discussed.
The meeting is expected to draw trade and investment from Brics members to Thailand, said a government spokesman.
The prime minister will touch on security issues and cooperation against terrorism, he noted. He is expected to share experiences on Thailand's sufficiency economy.
Gen Prayut was also due to meet Russian President Vladimir Putin and other leaders.