The brazen attack took place this morning in Incaville, near the city of Rouen in Normandy.

Inside the van was Mohamed Amra, known as The Fly, who was being driven through a toll booth on the way to prison when the van was attacked.

Our Europe correspondent, Nick Beak, reports.

An unremarkable toll booth in northern France and the scene of a swift and brutal ambush.

CCTV footage shows the moment a dark car veers into a white prison van and at least two masked attackers start shooting.

Terrified passengers on a passing bus throw themselves to the ground as the bullets ring out.

One assailant is seen strolling calmly among the other vehicles on the motorway.

Then here, you can make out the prisoner himself wearing white trainers as he emerges from the prison van.

The gang sets fire to their own vehicle, the smoke only adding to the chaos.

Some of them run towards another car, a white one, to begin their escape.

The aftermath, carnage.

Two prison officers dead, others gravely injured.

The gang then heads to the police station as their police colleagues begin a painstaking search for evidence in an attack that's been described as an assault on France itself.

They will be arrested, they will be judged and they will be punished commensurate to the crime that they have committed.

This is the man who was freed in the bloody assault, 30-year-old Mohamed Amra, a convicted local burglar.

But he was also the suspect in a fatal kidnapping in the southern city of Marseille, which is facing an onslaught of gang violence.

Amra and his accomplices are now being hunted by hundreds of police officers from here in Rouen as well as French special forces from across the country.

The burnt out vehicle that initiated the killing, a starting point for clues.

At the parliament in Paris, a minute's silence to honour the victims.

The prime minister conveying the sense of grief.

Our grief is that of an entire country, an entire country shocked by this attack of unprecedented violence, by the brutality and cowardice of its perpetrators.

Forensic and other specialist investigators spent hours at the scene of the ambush.

A violent attack on security staff is relatively rare in France.

So many have found the level of indiscriminate violence used today chilling.

Well, this also appears to have been a very well-planned ambush.

And 12 hours on exactly, we haven't got a clear sense of how the authorities are getting on in their search.

I think we can expect to see some raids in the coming hours, presumably on friends and family of the suspect.

But I think also what happened today, Sophie, shows us two things.

First of all, the criminal gangs in France do have access to really serious heavy weapons and are prepared to use them, not just on each other.

And secondly, it enforces, reinforces this worrying trend we've seen in the southern city of Marseille, where in the past year, more than 50 murders have been linked to gang crime there.

Troubling questions for the authorities in France, but tonight the priority is this manhunt, trying to apprehend the man they're calling public enemy number one.