NEW YORK (AFP) - Thousands of unidentified remains of victims of the 9/11 attack in New York were transferred in a solemn procession on Saturday to Ground Zero, the World Trade Center site that is now a memorial and museum.

The transfer drew protests from some families of the victims, who said it was an "insult" that remains possibly belonging to their loved ones were being put in an underground repository at the site of the 2001 attacks, which killed nearly 3,000 people.

The transfer was carried out in a somber procession of some 15 vehicles that left early Saturday from the New York Medical Examiner's Office on Manhattan's East Side.

Vehicles from the New York Police Department, the Fire Department and Port Authority of New York and New Jersey formed the cortege.

The remains were in metallic, rectangular cases.

"They were military transfer cases wrapped with the American flag. They were not coffins," police spokesman Carlos Nievas said.

Relatives of victims awaited their arrival at the Memorial Museum.

Of the 2,753 people declared missing at the World Trade Center site, 1,115 - or about 40 per cent of the total - have not been identified, according to the medical examiner's office.

Authorities recovered 21,906 human remains in the area, of which 7,930 could not be matched with the DNA of relatives of the victims.

One group of relatives at the site gathered to protest the move.

"We are outraged. There is anger and anguish. It's an insult and a sacrilege," said Ms Sally Regenhard, vice president of a group of relatives of 9/11 victims whose firefighter son was killed in the collapse of the World Trade Center.

"The city has refused to survey the families of the victims to get their opinion because they know the majority is against this plan," she said.

The repository is 20m underground and the public will not have access to it. It will remain under the control of the New York Medical Examiner's Office.

The 9/11 Memorial Museum above it will open to the public on May 21 although authorities have set aside five days beforehand for families of the victims, World Trade Center rescue and recovery workers and for survivors of the attack.