National flags in all government buildings including the Red Fort and Rashtrapati Bhavan fly at half-mast on Sunday as India observes one-day state mourning as a mark of respect to Britain's Queen Elizabeth II, who passed away on September 8.

People also paid respects to the Queen who became the United Kingdom's longest-serving monarch in 2015, when she surpassed the record of Queen Victoria, who had ruled from 1837 to 1901.

"Her Majesty Queen Elizabeth II, United Kingdom of Great Britain and Northern Ireland passed away on 8th September 2022. As a mark of respect to the departed dignitary, the Government of India has decided that there will be one day State Mourning on September 11th throughout India," an official statement of the Ministry of Home Affairs read.

"There will be no official entertainment on the day," the ministry said.

Britain’s longest-reigning monach, Queen Elizabeth II passed away on Thursday. She was 96.

Queen Elizebeth II came to the throne in 1952 and reigned for 70 years. Her reign spanned 15 prime ministers starting with Winston Churchill, born in 1874, and including Liz Truss, born 101 years later in 1975, and appointed by the Queen earlier this week.

Meanwhile, on Saturday, Prince Charles III was proclaimed as the king at a ceremony at St James's Palace on Saturday.