Britain's Queen Elizabeth II celebrated her 94th birthday on Tuesday, but the traditional gun salute was called off this year because of the coronavirus crisis.

The monarch was said to be marking the occasion with her 98-year-old husband, Prince Philip, at Windsor Castle, west of London. The couple, whose age puts them in a high-risk category for COVID-19, have been following the government's lockdown orders and maintaining social distancing rules during the pandemic.

Other senior royals have been housebound at their residences around Britain, so publicly wished the queen a happy birthday on social media instead.

"Wishing Her Majesty The Queen a very Happy 94th Birthday," her son and heir to the throne Prince Charles and his wife Camilla posted on Twitter alongside a selection of photographs of his mother through the decades. 

Buckingham Palace said on Saturday that the queen would not celebrate her birthday with a traditional gun salute given Britain's struggles to contain COVID-19. The country is among the worst-hit in the world by the virus, registering nearly 17,000 deaths in hospitals and almost 125,000 cases to date.

"Her Majesty was keen that no special measures were put in place to allow gun salutes as she did not feel it appropriate in the current circumstances," the palace said. The monarch made a rare national address at Easter, urging a collective response to the outbreak.