Graham Wettone said: "Police officers get calls like this every day about people being injured, so you are never quite sure what you are going to find.

"There's loads of stuff on social media already, that will form part of the line of investigation."

Read more:
Nottingham van attack: Follow latest updates
Three dead and man arrested after 'major incident' in Nottingham
Nottingham van attack: What we know so far

Nottinghamshire Police have arrested a 31-year-old man on suspicion of murder and he remains in police custody after three people were found dead after an apparent van attack in the city centre.

Detectives have said they are "keeping an open mind" and are working alongside terror police to establish the facts, as they normally would under the circumstances.

Investigators will be "trawling through social media accounts, witness accounts that have been posted onto social media, and just looking to see what evidence there is available, working through all possible options to see what's caused this, what's motivated this incident", Mr Wettone said.

He added: "People's perception of what they see in front of them can be very different.

"But it sounds like they have encountered a horrific incident in the early hours of the morning, and then a second incident, and possibly even a third.

"So it's a traumatic night for everybody involved."

Sudden arrival of armed police at lunchtime

At 1230 today, armed police rushed onto Ilkeston Road in the city. Officers had been called there just after 4am and two people were found dead in the street.

Hours later, at lunchtime, Sky News correspondent Becky Johnson was at the scene when more officers arrived. She said: "The road has suddenly been blocked off and traffic was allowed up there until just a few minutes ago.

"We're not sure what has happened but one would assume it is in connection with this major incident,"

Police were called to Ilkeston Road just after 4am where two people were found dead in the street.

Officers were then called to another incident in Milton Street where a van had attempted to run over three people. They are currently being treated in hospital.

A man was also found dead in Magdala Road.

Former Metropolitan Police officer Simon Harding said officers would be looking at "the risk of further offences" being committed.

'Officers will be at suspect's house'

He told Sky News: "There will be an enormous amount of work going on in the background... there will be officers linking in from other organisations such as counter-terrorism to understand if this is in any way linked to that.

"The main thing you want to do is get to the suspect's house, understand his associates, understand if there is any other risk associated with him and his actions today."

He said the police cordon remained vast - and would only be brought in after the understanding that everything "is under control".

"Scenes of this nature can take an enormous amount of time. Once they understand where those scenes really are concentrated in they'll start to bring in those cordons to try and bring Nottingham back to some sort of normality," he said.

"That won't be done until they are absolutely sure that they've got what they need and every bit of forensic evidence has been obtained and witnesses have been identified, CCTV that could help the enquiry to understand if there is anybody else involved, and all those sorts of things have been done."

Immediately after the call was received and officers were on site, he said the "main priority" would have been to save the lives of any victims.

"Then you want to try and get to those families as quickly as possible as well," he added.

Police interrogation

Sky News' crime correspondent Martin Brunt said police will be keeping an open mind in their investigations.

"People might be ready to jump to conclusions - that's the last thing that the police will do. And to some, this will have some of the hallmarks of a terror attack - but the key to this of course, is the suspect.

"Initially, at least, his motivation and his sense of ideology will be at the forefront of his interrogators' minds.

"They will be poring over everything about him - his mobile phone, his background, his home - if they've got to his home already - his friends and contacts. They'll be exploring all that in huge detail.

"Unless, of course, he is somebody who is in a position and prepared to talk to them.

"It may not be terror. We haven't had any kind of terror incident for the last two years at least. It may be a more explainable attack - a huge attack," he added.