LONDON -- An extensive report has found high levels of child abuse in England, with more than 2,400 victims during a 14-month period that was scrutinized.

The Office of Children's Commission interim study released Wednesday also found about 16,500 additional children are at "high risk" of sexual exploitation based on behavioural changes that were noted.

The report, which did not cover Northern Ireland, Scotland and Wales, is characterized as the largest ever study of child sex abuse in England, and suggested urgent action be taken to better protect vulnerable children.

"This report is a wake-up call," said Maggie Atkinson, Children's Commissioner for England. "Each and every one of us owes it to all victims to be vigilant, to listen and to act to stop the sexual exploitation of children."

The report follows a series of reports of "grooming" cases in which rings of men preyed on troubled underage girls.

It also comes after the police and the BBC have been sharply criticized for failing to take action against the late Jimmy Savile, an entertainer who has been alleged to have repeatedly abused young girls.

The commission found that abuse is greater than had been thought and that many sexual exploitation victims are not seen by professionals and do not have their cases recorded.

The report based its assessment of the number of children at risk on reports from police departments, local children's services boards and primary care units. It concluded that child sex abuse "goes largely undetected" for a variety of reasons, including inconsistent data collection that makes accurate reporting difficult. It also pointed out that there is no specific crime called "child sex abuse," making the crime difficult to track.

"It is not possible to state definitively how many children are victims of child sex abuse in any given period because there is no recognized category of abuse for sexual exploitation," the report said.