Six people, including three children, have been killed in a horrific knife attack on the normally tranquil isle of Jersey, off the southern coast of England, near France.

Police have arrested a 30-year-old man on suspicions he killed a man, two women and the children in an apartment in St. Helier, the capital of the island, the BBC reported.

The suspect is being held under police custody at Jersey General Hospital, where he is recovering from surgery.

The victims haven't been identified yet, but they are believed to all be related and also Jersey residents.

"Clearly this complex investigation is in its very early stages as we try to establish exactly what happened,” stated Detective Superintendent Stewart Gull, the head of crime services of States of Jersey Police.

"We are mindful, too, of the impact of any such serious and tragic incident on the local community, and we have police officers in the area to support the investigation and local people."

Gull added that the murders have been "pretty traumatic" for police investigators and emergency services personnel who were called to the scene.

"Dealing with multiple deaths of men, women and particularly young children, it has shaken the force but the officers who initially responded were tremendously professional," Gull said.

"Jersey is an incredibly safe island, probably one of the safest places in the western world. Incidents of this nature are an extremely rare occurrence."

The Home Affairs Minister of the island, Senator Ian Le Marquand, said Jersey residents will be in "shock and pain" after the fatal stabbings.

Police Chief Officer Mike Bowron commented: "It makes such a tragedy even more difficult for people to come to terms with, and no-one could fail to be affected by the events that unfolded here yesterday. Inevitably, perhaps, such an incident will raise tensions locally and I would appeal to everyone to remain calm and dignified and allow my officers to continue with what is a complex, demanding and difficult investigation."

Police investigators from Devon and Cornwall in England will also help with the investigation.

The island has historically been very safe. According to reports, more than 4,500 crimes were reported in Jersey last year, about half of them theft, burglary, fraud and forgery.

Jersey, which is part of the Channel Islands, has a population of about 91,000, the majority of whom are of Norman French and British ancestry. As Crown Dependencies, the islands are not part of the UK, nor the European Union.