Thailand’s King Maha Vajiralongkorn is due to arrive in China on Thursday, the first ever visit by a reigning Thai monarch.

The visit is at the invitation of Chinese President Xi Jinping to celebrate the 50th anniversary of both countries establishing diplomatic ties in 1975. China is believed to have been pushing for this visit for some years.

Thailand is still officially a military ally of the US, but relations with China have grown steadily closer in recent years.

In contrast, those with Washington have been frayed by US criticism of human rights in Thailand, by US President Donald Trump’s tariffs, and a perception that the US is no longer as committed as it once was to its Asian friends.

In a statement, the Thai government said the trip “underlines the deep-rooted friendship and mutual understanding shared between Thailand and China at all levels”.

During his trip to the capital Beijing, the king and his wife Queen Suthida will visit local landmarks like the Lingguang Buddhist Temple and the Beijing Aerospace City.

President Xi and his wife will also host a state banquet for the Thai royals.

China is Thailand’s biggest trading partner, and increasingly a rival to the US as a source of military equipment.

Many Thais can trace their ancestry to migrants who came from China, and the Chinese government often highlights what it calls their ‘brotherly’ of ‘family’ relations.

The importance of those ties to Thailand was underlined earlier this year when the Thai authorities deported 40 Uyghur asylum seekers back to China, in defiance of a warning not to do so by US Secretary of State Marco Rubio.

Then in August an exhibition at Bangkok’s main arts centre featuring Uyghur and Tibetan artists was censored following complaints by Chinese diplomats.

The Thai government has also been spurred by Chinese pressure into taking action against scam compounds operating along its border with Myanmar, and objections by China are presumed to have been one of the factors which blocked a proposal to legalise casinos in Thailand.

This will be the first major state visit by King Vajiralongkorn since he came to the throne nine years ago – in April he had made an inaugural trip to Bhutan.

This was reflected in the high-profile overseas trips made by his father King Bhumibol Adulyadej were to the United States in the 1960s, when Thailand was feted as a crucial Cold War partner, and a vital base for US military operations in Indochina.

But the king’s younger sister, Princess Sirindhorn, has played a crucial role in restoring and sustaining Thai-Chinese relations since.

The princess has studied Chinese art and language for the past 45 years, and been a frequent visitor to China.