Nearly a third of female rape victims are girls aged under 16, new figures indicate.
The findings emerged as the first detailed breakdown of the age and gender of victims of alleged sexual offences recorded by police were published.
Experimental data, published by the Office for National Statistics (ONS) and based on statistics from 13 forces in England and Wales, showed that in the 12 months to March last year:
::Three in ten (30%) female rape victims were aged under 16, a quarter (25%) were 14 or younger and nearly one in ten (9%) were nine years old or under.
::Rape victims of both sexes were most likely to be aged between 15 and 19.
::Half of female victims of other sexual offences, such as assaults, grooming and sexual exploitation, were girls aged under 16.
Sarah Green, of the End Violence Against Women Coalition, said the statistics are "truly alarming".
She said: "They have to be a wake up call to the Government, to every profession working with young people and to all of us - what are we going to do about this horrific level of assault against young women and girls?
"We believe the figures show that those who commit these crimes target victims who are young and more vulnerable. Offenders have more confidence in getting away with crimes against younger women and girls.
"We have to get serious about tackling the perpetrators of this abuse and preventing assaults in the first place."
Analysis of the Crime Survey for England and Wales published alongside the statistics showed that respondents in younger age groups were more likely to think it was acceptable at least some of the time to hit or slap their partner if they have an affair.
Ms Green said: "It is clear that many young people have extremely worrying attitudes towards acceptable behaviour in intimate relationships.
"We cannot ignore the easy availability of online pornography and other parts of popular culture with its messages about jealousy, ownership and traditional male and female roles, and we need a debate about this."
The ONS said the overall number of sexual offences logged by police in the year ending March last year, 88,106, was the highest tally since the introduction of crime recording standards in 2002.
It said: "As well as improvements in recording practices, this is thought to reflect a greater willingness of victims to come forward to report such crimes."
Mark Castle, chief executive of charity Victim Support, said: "While the increase in reporting and better police recording of sexual crime is to be welcomed, there is still a long way to go in improving the support given to victims who make the brave decision to speak up and seek justice."
The ONS also said that improvements in crime recording processes by the police are thought to be the main driver behind a 23% rise in the number of violence against the person offences recorded.
David Tucker, of the College of Policing, said: "It's encouraging to see that improved recording practices in forces are believed to be behind the increase of recorded violent and sexual crimes."
He added: "However, there are still too many violent and sexual crimes.
"Our research on national demand has indicated an increasing amount of time in forces is directed towards public protection and safeguarding issues."