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

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, according to BBC.