LONDON, United Kingdom -- Queen Elizabeth II returned to London to resume public duties on Monday following a health scare as the capital echoed to the sound of cannon shots to mark her 70 years on the throne.

At midday (1200 GMT), the King's Troop Royal Horse Artillery unit fired a 41-gun salute from Green Park, near the monarch's Buckingham Palace residence in central London, beginning a year of celebrations to honour Britain's longest-serving monarch.

Another 62 shots then rang out an hour later from the Tower of London, the historic royal palace and home to the Crown Jewels three miles (five kilometres) across the city.

The ceremonies took place the day after "Accession Day", the date in 1952 when Princess Elizabeth's father king George VI died and she became queen.

"For me this is the launch of the Platinum Jubilee, this is where it all starts for all of us and as a country," said Lieutenant Colonel James Shaw, who oversees the army's ceremonial events.

"On June 2 we've got the Queen's Birthday Parade, with 1,400 troops involved in that, and on June 5 there's the pageant and the armed forces will also be involved," he added.

The Green Park salute consisted of the usual 21-gun salute with an extra 20 due to it being in a royal park. There were another 21 shots at the Tower of London event as it is in the City of London.

- Life of service -
The four-day jubilee weekend will begin on Thursday June 2, although events will be held throughout the year to honour the 95-year-old queen.

Elizabeth on Sunday became the first British monarch to reign for 70 years, marking the historic date quietly at Sandringham, her estate in eastern England where her father died.

She has barely been seen in public since being laid low by a health scare in October, which required an overnight hospital stay for preliminary tests.

Stressing that the Queen is still actively working, Buckingham Palace released a photo taken at Sandringham this week showing her going through one of her famous red dispatch boxes used for government business.

She also held a reception on Saturday for locals at Sandringham, which was reportedly her largest in-person public engagement since the autumn scare.

Buckingham Palace on Monday told AFP that the Queen had returned to her Windsor Castle residence, west of London, and was resuming public duties, which it is hoped will include attending a thanksgiving service for her late husband Prince Philip at Westminster Abbey on March 29.

"In addition, her majesty will be resuming her normal duties of audiences, credentials and privy council meetings, continuing to mix both virtual and in-person events," a source told the domestic Press Association.

She plans to attend a diplomatic reception on March 2 and the annual Commonwealth Service at Westminster Abbey on March 14.

The four days of festivities in early June coincide with the anniversary of her 1953 coronation, including a military parade and music concert, street parties, a nationwide "Big Jubilee Lunch" and a "Platinum Pudding Competition".

In her message addressed to the public signed "Your servant, Elizabeth R", the Queen renewed a pledge she first gave in a broadcast on her 21st birthday "that my life will always be devoted to your service".