Britain's Queen Elizabeth has become the second-longest serving monarch in world history.

BBC and other British media have reported that as of Monday, the Queen has been on the throne for 70 years and 127 days. She overtook Thailand's King Bhumibol Adulyadej, who died in 2016, having equaled his reign on Sunday.

The Queen is now second to King Louis the 14th of France, who reigned for 72 years and 110 days, between 1643 and 1715.

The Queen became monarch at the age of 25, following the death of her father in 1952. She became the longest-reigning British monarch when she surpassed the reign of Queen Victoria in 2015.

The milestone comes as Britain observed a series of Platinum Jubilee events this month to celebrate her 70 years on the throne.

The 96-year old Queen's absence from some of her official duties, as well as her use of a walking stick, are raising concerns over her health.