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Emergency services treats victims near Westminster Bridge and the House of Parliament in London, England, Mar. 22, 2017. Getty Images

An attack Wednesday at the Parliament building in Westminster, London, left at least one person shot, a police offer stabbed and an untold number of injuries. Metropolitan Police said the attack was being treated “as a terrorist incident” until they confirmed otherwise. Meanwhile, Queen Elizabeth II remained nearby.

“The Royal Standard is flying over Buckingham Palace which means the Queen is just half a mile from this possible terrorist incident,” ITV News Royal editor Chris Ship tweeted shortly after the incident.

Read: Gunshots, Injuries Reported In Attack On London Parliament In Westminster

The Royal Standard flag signals to the world that the queen is currently at the royal residence.

For her protection, the queen is continuously flanked by armed guards from SO14, the Royalty Protection Branch of the Metropolitan Police. However, her security would likely be stepped up in the wake of an incident like the one in Westminster. In September 2015, security was enhanced for the monarch following attacks on British jihadis in Syria, the Telegraph reported. In addition to SO14 officers, the queen was accompanied by plain-clothed officers, armed police on the ground and rooftop marksmen during her travels.

“Security is always arranged in layers, starting with the close protection bodyguards and then in concentric rings, like an onion skin,” Dai Davies, former head of Royal Protection, told the Telegraph. “Additional layers will be added as appropriate, according to the intelligence available.”

Davies noted that the threat level to the queen would be assessed in similar situations and the level of security decided on from there.

During the attack, at least one person was shot by police after an officer was stabbed outside the House of Commons. Meanwhile, a car had driven into a crowd of people on Westminster Bridge. One eyewitness told Sky News he saw a body in the Thames River. Doctors confirmed that numerous pedestrians had been injured and at least one had been killed.

“I confirmed one fatality. A woman. She was under the wheel of a bus. She died, confirmed her death at the scene,” Colleen Anderson, a junior doctor at St. Thomas’ Hospital told reporters. “There were people across the bridge. There were some with minor injuries, some catastrophic. Some had injuries they could walk away from or who have life-changing injuries. There were maybe a dozen injured.”

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Emergency services treats victims near Westminster Bridge and the House of Parliament in London, England, Mar. 22, 2017. Getty Images