Prime Minister Boris Johnson is expected to lead the tributes to Queen Elizabeth II on Tuesday, as Britain's longest-serving monarch turns 94.

The queen, who has ruled Britain for more than 68 years, is not expected to attend any public events amid Britain's near-lockdown to curb the spread of novel coronavirus.

The royal family announced that an annual military parade of horses and gun carriages past Buckingham Palace, the queen's London home, and traditional gun salutes marking her birthday have been canceled this year.

The queen and her husband Prince Philip, 98, left London for Windsor Castle last month as a "sensible precaution" amid the coronavirus pandemic, the palace said.

The queen's eldest son and heir, Prince Charles, 71, self-isolated at one of his homes in Scotland after he tested positive for the virus and experienced mild symptoms.

Tuesday's anniversary marks the actual date of the queen's birth, while more events normally take place in June to mark her official birthday.

Born in 1926, the queen has ruled since 1952, when she was 25 years old.

In 2015, she surpassed the six-decade reign of Queen Victoria, her great-great-grandmother, from 1837 to 1901.

Britain's system of constitutional monarchy keeps the queen as a largely ceremonial head of state, allowing the government to pass legislation and run the country.