Police in the North East have sent their thoughts and prayers to the Metropolitan Police after yesterday's attack on the Palace of Westminster.
Four people, Pc Keith Palmer, the man responsible for the tragedy and two members of the public, died in the incident, which has left around 40 people hurt.
Northumbria, Durham and Cleveland have all changed their profile pictures on social media to the Thin Blue Line Union Jack, used by police in tribute.
Flags at police stations have also been lowered to half mast, as were those at council offices.
Cleveland has also said it took part in a minute silence at 9.33am "to pay our respect to the victims of yesterday's attack at Westminster" after the Cabinet Office would be held in Whitehall.
Northumbria Police said: "For our friends and colleagues in London. #policefamily."
Today, Temporary Assistant Chief Constable Vanessa Jardine, said: "Following yesterday's tragic incident in London our thoughts are with the people affected and their families.
"We want to remind people that the national threat level remains at 'severe' but there is still nothing to suggest any specific threat to our communities here in Northumbria.
"Armed patrols have been taking place across our region since last year and those patrols will continue following this most recent incident.
"This will include patrols conducted in our areas with high numbers of people, such as the city centres and our transport hubs.
"Those patrols are in place to reassure any members of the public concerned about security in our force area.
"It is very important at times like these that our communities come together and support each other.
"I would encourage anyone who sees anything suspicious or who has any concerns to report them immediately."
The force's police federation, which represents officers said on Facebook: "The thoughts of all at Northumbria Police Federation and the officers we represent our with Keith's family, friends and close colleagues.
This morning, Steve White, chairman of the federation across England and Wales said: “No words can capture how members of the policing family will feel after today’s horrific events,”
“We have lived in the knowledge that an attack on UK soil has been highly likely for nearly three years.
"Everyone is firmly aware of this fact, but it makes it no less shocking when it becomes a reality.
“This incident highlights the very real risks that police face each and every day.
"Officers will take the opportunity to hug loved ones and seek comfort in the company of friends and family.
"But one will not. The pain of that officer’s family, friends and colleagues will be shared by us all.
“Our hearts go out to their family and our thoughts are with them and their colleagues at this terrible time along with others who have been injured.”
Durham Constabulary said last night: "Our thoughts tonight are with Metropolitan Police Service colleagues, family and friends of the victims and all those involved in today's attack in Westminster.
"If you are worried about family or friends who may have been involved in today’s incident please call the Casualty Bureau on 0800 056 0944 & 0207 158 0010. Demand will be high so please be patient."
This morning, Deputy Chief Constable Jo Farrell said:
Durham Constabulary Deputy Chief Constable Jo Farrell said: “Our sympathies go out to all those affected by the tragic events in London and to the family of Pc Keith Palmer and those who lost their lives.
“The public's safety remains our top priority.
"I want to reassure the people of County Durham and Darlington that there is no specific information suggesting an imminent threat to our communities.
“There has been no change to the current threat level for international terrorism in the UK which remains at 'Severe' and which means ‘an attack is highly likely’.
“I would like to stress that it is very much business as usual.
"There will be extra patrols by uniformed officers at key locations but this is merely a reassurance measure.
“We urge people to be alert but not alarmed. It is also incredibly important at times like this that communities come together and support each other.
“Should anyone have any concerns or see anything suspicious I would urge them to report it immediately to the Confidential Anti-Terrorist Hotline on 0800 789321. In an emergency always dial 999.”
The force added "If you wish to learn first aid skills which may be used in a terrorist attack download the CitizenAID app
Cleveland Police said: "Our thoughts tonight are with those affected by events in Westminster, including our Metropolitan Police colleagues and family."
Cleveland Police Federation said on its Facebook page: "Today, whilst we all mourn the loss of Pc Keith Palmer, we also remember the three other officers critically injured yesterday in the cowardly attack in Westminster."
Assistant Chief Constable Ciaron Irvine said: "Despite these events the local threat level, mirroring the national threat, has not changed and we have no specific intelligence to suggest any links to the Cleveland force area.
"However, we understand that there may be increased concerns among local residents and are increasing the visibility of neighbourhood patrols to offer reassurance to all of our communities.
“Anyone with concerns or anyone who would like more information can refer to the Cleveland Police website for further advice on www.cleveland.police.uk.”
South Tyneside Council was among those to take part in the minute's silence and lowering of flags.
Council leader Iain Malcolm tweeted: "Flags at half-mast across South Tyneside and staff and members observed a minute's silence this morning."
Please see below a statement from the Mayor of South Tyneside:
The mayor of South Tyneside, Councillor Alan Smith, said: “Our thoughts are with the people of London and indeed the entire UK at this tragic time.
“We stand in solidarity with all those working and living in the capital. The flags at both Jarrow and South Shields town halls are flying at half-mast as a mark of respect and a minute’s silence was observed by elected members and staff of South Tyneside Council, South Tyneside Homes and BT South Tyneside this morning.
“As a nation we will not stand for such an attack on citizens in the UK or any country in the world. Our thoughts are with all those affected by these atrocious events.”
Durham County Council also joined in the effort, as did Hartlepool Borough Council, which held a silence as well as lowering its flag.
It said: "This morning #WeStandTogether with #London after yesterday's #Westminster attack.
"As a mark of respect we are flying the union flag at half mast over#Durham County Hall and council buildings."
Sunderland Coastguard Rescue Team shared Maritime and Coastguard Agency's video on its Facebook page.
It said: "Our thoughts are with all those effected by the terrible events in Westminster yesterday and with the Metropolitan Police who lost one of their own in the line of duty."
Tributes have also been paid in the region to Pc Palmer, 48, who died in the attack.
Heather Fagan said: "He gave his life to save others.
"Thinking of his family at this sad time, he died a hero."
Lesley Wraith posted: "RIP Keith Palmer, my thoughts go to his wife and children and family members."