The Death Gun Salute is fired by the Honourable Artillery Company to mark the passing of Britain's Prince Philip in London. AFP

Philip, the longest serving royal consort in British history and a constant presence at the queen's side for decades, died on Friday aged 99, triggering a period of national mourning.

The death of the Duke of Edinburgh is a profound loss for the 94-year-old monarch, who once described her husband of 73 years as her "strength and stay" throughout her long reign.

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Flags are already flying at half-mast on government buildings and will do so until the morning after his funeral, the date of which has yet to be announced.

Britain's Prince Philip arrives on the eve of his 90th birthday in London. Reuters

From 12:00 pm (1100 GMT), saluting batteries will fire 41 rounds — one round a minute for 40 minutes — in cities including London, Edinburgh, Cardiff and Belfast, as well as in Gibraltar and from Royal Navy warships at sea.

The Premier League and other sporting events are expected to pay their respects, with the Football Association recommending that black armbands be worn and a minute's silence observed before this weekend's matches.

A two-minute silence will be held ahead of Saturday's Grand National, the country's showpiece horse race.

The well-rehearsed protocol for the duke's death — codenamed "Forth Bridge" — includes the recall of parliament on Monday.

A box of empty shells is prepared for a gun salute to commemorate the death of Britain's Prince Philip in London. AFP

British television stations cleared their schedules for special broadcasts looking back on his life, although the BBC said it had received complaints about the blanket coverage.

Westminster Abbey, where the couple married in 1947, tolled its tenor bell 99 times on Friday, once for each year of the prince's life.

Political campaigning for May local elections stopped, and Loyalist leaders in Northern Ireland, who have been rioting for days amid heightening political tensions in the British province, urged a pause in violence on Friday.

The call -- "as a mark of respect to the Queen" -- was largely heeded.

Marches that had been planned by members of the pro-UK unionist community in Belfast were cancelled n Saturday.

But despite the calls for calm, some lower-level disorder continued overnight.

Agence France-Presse