A hospital in Versailles, near Paris had to cancel operations and transfer some patients after being hit by a cyberattack over the weekend, France's health ministry said Sunday.

Six patients had been transferred by Saturday evening -- three from intensive care and three from the neonatal unit -- said the minister, Francois Braun, as he visited the hospital. Others might follow, he added.

The regional health agency (ARS) said the hospital had cancelled operations but was doing everything possible to keep walk-in services and consultations running.

Extra staff had to be called in to the intensive care unit because, while the machines there were still functioning, more people were needed to watch the screens as they were no longer working as part of a network, aid Braun.

The cyberattack had led to a "total reorganisation of the hospital", the minister added.

The Paris prosecutor's office has opened a preliminary investigation into hacking state data and attempted extortion after the hospital filed a formal complaint Sunday.

For several months now, hospitals and health systems in France have been targetted by hackers for such cyberattacks.

According to Braun, the same hospital had already seen off cyberattacks in recent months.

In August, the Corbeil-Essonnes hospital on the outskirts of Paris was also targetted, taking several weeks to get back to normal functioning.

On that occasion, the attack was followed by a demand for 10 million dollars, subsequently lowered to one or two million dollars.

The hackers set a September 23 deadline for the hospital to pay the ransom, after which they posted confidential data on patients and staff to the "dark web".