A three-day counter-terrorism exercise testing the response of emergency services in England and Scotland to a cross-border incident has begun.
The North East Ambulance Service, Northumbria Police and the Tyne & Wear Fire and Rescue Service were among those taking part of in the "live-play scenario", which will involve locations in the Lothians and Northumbria. It is not in response to any specific threat but the result of more than a year of planning.
Police Scotland Assistant Chief Constable Bernard Higgins said training needs to respond to the change in high-casualty attacks carried out by individuals or small groups with vehicles and weapons such as has been seen recently in the UK.
The exercise featured a vehicle attack which began in an area of the Royal Bank of Scotland headquarters in Edinburgh on Tuesday morning.
It tested armed response teams, paramedics and firefighters as well as police control room and organisational staff as observers watched the action unfold.
Home Secretary Amber Rudd chaired a COBR meeting as part of the exercise and the Scottish Government's Resilience Room updated Scottish ministers on the event.
Named Exercise Border Reiver, police said it will not affect day-to-day policing or emergency responses, which will continue as normal throughout the exercise.
Mr Higgins said: "We've seen a number of terrorist incidents within the UK which sadly led to a lot of fatalities. We've moved to a threat level of critical on two occasions.
"As these things have occurred so have our plans evolved to try and recreate the threat that we believe exists within the UK.
"In previous exercises the attacks were more coordinated, so you have had two or three different cells attacking different venues at different times.
"What we've seen in recent times - particularly in the UK - it's low sophistication, it's small numbers of people, often lone actors. They're using vehicles, they're using knives and bladed weapons, but the impact is high and the casualties are high.
"So it's trying to recreate what we believe will be a likely scenario, should it occur."
He added: "This is an exercise - it's not because we know something is going to happen or we believe something is going to happen. There is absolutely no intelligence to suggest that Scotland is going to be a specific target of terrorism at any point in the future.
"People in the Edinburgh area today and over the next few days, please don't be alarmed if you see lots of blue lights and sirens or if you hear gunshots.
"It is blank cartridges we're using, but it's trying to recreate the pressure and the tension that the first responders will be feeling at the scene and the senior officers and staff will be feeling back in the operations room."
Other bodies involved in the three-day exercise include the Scottish Fire and Rescue Service, Scottish Ambulance Service, Northumberland Fire and Rescue Service, Transport Scotland, NHS Scotland, NHS England and the Ministry of Defence.
City of Edinburgh, Angus and Northumberland County councils are also testing their responses to a terrorist incident.
The Home Secretary said: "The events of this year have shown why it is vital that the emergency services, Government and agencies prepare and rehearse our response to potential terrorist attacks.
"The professionalism with which front line services dealt with the atrocities in London and Manchester is in part due to the planning and practice that goes into exercises like this."
Officers said they will inform people in local residential and business areas close to the exercise so as not to raise alarm through noise or a large presence of emergency services.
Assistant Chief Constable Darren Best of Northumbria Police said: "This exercise has been organised to test the response of the emergency services and other partner agencies to a cross-border incident. It is in no way linked to a specific or increased threat in our region.
"We regularly carry out exercises to test contingency plans and the co-ordination of the response to a major incident to ensure we are prepared to keep our communities safe."
Scotland's Cabinet Secretary for Justice Michael Matheson said: "Scotland has a key role to play in hosting this exercise, alongside the UK Government and other agencies.
"It provides an opportunity to test our response in Scotland and the readiness of our emergency services to deal with this kind of incident.
"The Scottish Government shares the commitment of our partners to taking all necessary steps to assess and strengthen our preparedness to deal effectively with terrorism.
"While fortunately such real life incidents are rare, the public can be assured that government, our blue-light services and other agencies are continuously testing and reviewing how we are best able to respond to an attack should it happen."