A man has been shot dead by police as he approached them brandishing a sword on the A63 near Hull.
The man got out of his van brandishing a sword, witnesses say
Police tried to stop Simon Murden, 26, from Beverley, by firing baton rounds but these failed, said Humberside Assistant Chief Constable John Crosse.
It is the first time in the force's history that officers have fired during an incident.
The Independent Police Complaints Commission (IPCC) is to conduct an investigation.
Police had sent armed officers to the area after they were told a van was being driven in the wrong direction near Welton at 0620 GMT.
Mr Crosse told a news conference: "As is force procedure, the deployment of armed officers was authorised by a chief officer.
"It is reported that the man began to approach the police officers.
"Baton rounds were fired but they failed to stop the man in his approach. A conventional firearm was then used and the man was hit."
Police closed off the A63, which is a continuation of the M62 and the main route into Hull from the west, until early evening.
A major investigation at the scene is being carried out near a Little Chef restaurant and a petrol station at the side of the dual carriageway about 10 miles west of Hull.
Two senior investigators from the IPCC are at the scene.
"Their purpose is to find out exactly what happened and then recommend to our commissioner Nicholas Long how the investigation should proceed," an IPCC spokesman said.
House sealed off
The local MP, Shadow Home Secretary David Davis, has been given a briefing by police on what happened.
The road was closed while police examined the scene
He said police tried to resuscitate the man but he was found to be dead.
Eyewitness Paul Hankinson told BBC News he had seen a police car pursuing the van down the A63.
"The next minute we heard this almighty bang and we thought 'what the hell was that?'.
"We thought that's someone behind us.
"The next minute we saw that van behind us coming up facing the wrong way towards the carriageway followed by a cop car."
The van came from a charity shop in nearby Beverley. A sign on the door of the shop said it was closed because of a bereavement.
The 'And Albert Foundation' shop in Beverley sells Fair Trade goods and has its own "Trading Roots" labelled products.
Police have sealed off a house in Beverley in connection with the incident.