The medics treating the scores of victims in the Paris terror attacks came back without their belts — so great was the need in the field for tourniquets, medical personnel said Tuesday.

And when the wounded began to arrive at the city's hospitals some doctors thought it was the extension of a drill carried out earlier the same day to practice their response, in a cruel irony, to a mass shooting.

The harrowing details come from the most detailed recounting yet of the response inside Paris's massive medical system as it was hit by France's worst terror attacks.

“We didn't know how and when this nightmare would end,” said an emergency doctor in the account published in The Lancet medical journal.

The Paris hospital system first learned of the coming horror on November 13 around 9:30 pm, when it was alerted to the explosions outside the Stade de France, where three suicide attackers blew themselves up.

Then came word of the shootings at the Bataclan concert hall as well as at bars and restaurants in a hip neighbourhood of east Paris, where nearly all the 130 victims were killed.

“Despite their brutality and appalling human toll, the attacks were not a surprise,” the doctor said.

Following the deadly shootings at satirical paper Charlie Hebdo and a Jewish grocery 10-months prior, “all state departments had known that a multi-site shooting could happen.”

An hour after the first warning, the hospital system called in all staff to deal with the wave of patients. Many physicians and nurses had already turned up spontaneously to help.

The wounded, most of them under the age of 40, came pouring in. Most had most bullet wounds. And many needed surgery, quickly.

“Never before had such a number of victims been reached and so many wounded been operated on so urgently,” according to the account.

“A new threshold has been crossed.”

Patients arrived in groups and were triaged even before they were inside the hospital. Within 24 hours all emergency surgeries had been completed.

“The hospital was nearly ready to cope with another attack that we all feared could occur,” said an anaesthesiologist.

The timing of the attacks may have played a role in the ability to mount a massive medical response. During the working day doctors and staff would have been busy already.

Nearly every patient who made it to the hospitals — either by ambulance or under their own power — survived.

But not all of them. Doctors recorded four deaths, two of them on arrival at the hospital.