The Queen arrived in the Republic of Ireland on Tuesday to start the first visit by a British monarch in a century.

Accompanied by Prince Philip, she touched down at Casement Aerodrome, south-west of Dublin, at 11.55am local time to start the historic four-day visit, which is taking place amid a huge security lockdown.

The jet taxied with the sovereign's standard, which bears an Irish harp, flying from the cockpit window. Two lines of troops formed a guard of honour either side of the red carpet at the aerodrome.

The Queen wore a blue dress beneath an Irish emerald green coat and hat, while the Duke of Edinburgh wore a dark business suit. She smiled broadly as she was welcomed by dignitaries before receiving a posy of flowers.

The former Baldonnel military airbase, home to Ireland's Army Air Corps, was renamed in 1965 after Roger Casement, an Irish nationalist executed for treason by the British in 1916.

Police had lined the airbase perimeter throughout Monday as the authorities combed through the bushes outside and along the road into Dublin.

The trip, aimed at reconciliation between an independent Ireland and its former ruler, Britain, is taking place amid the biggest security operation in the Irish state's history.

Queen makes history in Ireland amid security fears