Queen Elizabeth officially becomes longest-reigning British monarch

With sundown in Britain on Wednesday, Queen Elizabeth II officially became the longest-reigning British monarch after passing the record set by her great-great-grandmother Queen Victoria, the media reported.

The Queen, who has served 63 years and 216 days on the British throne, officially broke the record at 5.30 p.m. local time (10 p.m. India time) on Wednesday, the Guardian reported.

As she reached the historic milestone, the Queen, along with Duke of Edinburgh and Scotland's first minister, Nicola Sturgeon, boarded a steam train in Edinburgh to officially open the Scottish Borders Railway.

While declaring the borders railway open, she said: "The Duke of Edinburgh and I are delighted to be back in the Borders today and especially to have arrived by train. It is wonderful to have witnessed the excitement which the return of the railway has brought here."

The Queen then thanked those around the world for their "touching messages of great kindness".

"We are very grateful for the warmth of your welcome on this occasion. Many, including you, First Minister, have noted another significance attached to today. Although it's not one to which I've aspired. A long life can pass many milestones. Mine is no exception," the Queen said in a statement.

According to a BBC report, Prime Minister David Cameron will lead tributes in the House of Commons and there will be a River Thames salute to mark the occasion.

On the Thames, a flotilla of historic vessels, leisure cruisers and passenger boats will take part in a procession between Tower Bridge and the Houses of Parliament.

The bridge will lift as a sign of respect and H.M.S. Belfast will fire a four-gun salute.

The BT Tower in central London will scroll the message "Long may she reign".

She has let it be known that she does not want a fuss to be made. It is evidently viewed as bad form for one long-lived queen to be celebrating the passing of a record set by another long-lived queen.

The prime minister's official spokeswoman said David Cameron had paid tribute to the Queen at a cabinet meeting on Monday.

He said the Queen had a "remarkable record" and was "a symbol of Britain's enduring spirit admired around the world".

Queen Elizabeth's reign has included 12 prime ministers, two more than served under Victoria.