Britain’s Queen Camilla has pulled out of attending Tuesday’s funeral service for the Duchess of Kent as she recovers from acute sinusitis, Buckingham Palace said.

The queen, King Charles’ wife, is hoping to have recovered sufficiently to attend all the planned engagements for the state visit by US President Donald Trump which begins at Windsor Castle on Wednesday, a royal source said.

Camilla, 78, travelled down from Scotland and is resting at Windsor Castle where the state visit will be held.

She had been scheduled to join the king and family members at the funeral service at London's Westminster Cathedral for the duchess who died on September 4.

"Her thoughts and prayers will be with the Duke of Kent and all the family," a Palace spokesperson said.

Camilla is due to play a prominent role during the visit by Trump and his wife Melania, including taking part in a carriage procession and attending a lavish state banquet.

On Thursday, she is set to give Melania a tour of the castle's Royal Library and the famous Queen Mary's Dolls' House, reputedly the largest in the world which celebrated its 100th anniversary last year.

Last year, Camilla was forced to pull out of a number of engagements after suffering a chest infection, while Charles, 76, himself is still undergoing treatment for cancer, meaning his workload has to be carefully managed.