Police are appealing for witnesses and motorists with dashcam footage to come forward following a crash between a double decker bus and a lorry on the A47 near Thorney Toll this morning.
The driver of the bus, a man in his 50s from Norfolk, and a passenger, a man in his 70s from Northampton, died at the scene.
Five other passengers suffered serious injuries, including broken bones and head injuries, while seven other people on board were also wounded.
Inspector Jamie Langwith confirmed none of the seriously injured passengers were wearing seat belts at the time, but could not state whether this included the driver.
He said: "We don't believe the five who were seriously injured were wearing seat belts.
"It is not confirmed if the bus driver was wearing a seat belt."
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Inspector Langwith said no children were on board the bus at the time of the crash.
He added: "We were called to a two-vehicle collision where upon a bus has collided with a HGV lorry from Brett’s Transport where in fact they have collided together upon the junction.
"On arrival here there were a number of injuries, sadly two fatal. The lorry driver is not injured.
"We have a number of witness statements but we are appealing for more witnesses especially with dashcams.
"We are currently unloading the HGV so the investigators can do what they need to do."
Around 20 police vehicles could be seen at the scene along with ten ambulances and four engines.
Motorists in the area at the time of the crash described low-lying sun and fog, which made it difficult for the air ambulance land.
Frank Fowler, a farm contractor who was travelling near the A47 this morning, said: "After 7am this morning it was still very foggy and fairly hazy.
"It was patchy but at some points you still needed your headlights on because the visibility was very poor.
"It could have affected the any driver's vision."
However, Inspector Langwith confirmed weather conditions were not being considered as a contributing factor to the crash.
Cambridgeshire’s Police & Crime Commissioner posted a tribute to those involved in today’s incident.
Jason Ablewhite said: "I would like to express my heartfelt sympathy to those affected by today’s tragic event on A47.
"I want to thank the emergency services who worked together to manage the incident, making sure those injured were taken to safety."
Inspector Langwith added: “People are in shock because they are not quite sure what happened.
“It is a very sad incident and it’s never easy for police to deal with these incidents.
“The police are liaising with the families to help them get through this really terrible time.”
Relatives of those involved are being updated by officers at Peterborough City Hospital and Queen Elizabeth Hospital in Kings Lynn, Norfolk.
It has also emerged that the bus driver who died in the crash was from Norfolk and worked at the First bus depot in Kings Lynn.
Steve Wickers, Managing Director at First Eastern Counties said: “As confirmed earlier today, one of our buses was involved in a fatal road traffic incident with a lorry on the A47 in Guyhirn.
“Two people have lost their lives in this incident, one being a driver based in our Kings Lynn depot.
“I am shocked and saddened by what has happened. Our thoughts are with the families of the deceased and we will be providing as much support to them as we can through this difficult time.
“A further 18 people on the bus sustained injuries and have been cared for by the emergency services at the scene.
“We will now be working with the police while they undertake their investigations.”