Seven independence activists accused of inciting deadly riots in New Caledonia have been sent to mainland France for pre-trial detention, a local prosecutor said Sunday.

"This transfer was organized during the night by means of a plane specially chartered for the mission," Yves Dupas, the public prosecutor in the territory's capital Noumea, said in a statement.

The seven were sent to mainland France, he added, "due to the sensitivity of the procedure and in order to allow the investigations to continue in a calm manner, free of any pressure."

Among the seven detainees was Christian Tein, head of the pro-independence group CCAT, who was charged Saturday over the recent violence in which nine people died, including two police.

Hundreds more were wounded, and around 1.5 billion euros ($1.6 billion) of damage was inflicted during the unrest over controversial voting reforms.

Authorities did not immediately specify what charges Tein faces.

His lawyer Pierre Ortent said Saturday he was "stupefied" that his client was being sent to France, accusing magistrates of "answering to purely political considerations."

Riots, street barricades and looting broke out in New Caledonia in May over an electoral reform that would have allowed long-term residents to participate in local polls.

The archipelago's Indigenous Kanaks feared the move would dilute their vote, putting hopes for eventually winning independence definitively out of reach.

France's government repeatedly accused Tein's CCAT of orchestrating the violence, a charge the organization has denied.