The number of UK-born children thought to have been trafficked for sexual exploitation more than doubled last year, the National Crime Agency said.
Fifty-six minors from the UK were flagged up as potential victims of trafficking for sexual exploitation in 2013 - a rise of 155% on 2012.
It is unclear whether they were being taken out of the country or moved within the UK, the NCA said.
The government said it was unlikely the data reflected the scale of the issue.
The NCA data suggested the number of foreign children identified as potential victims of trafficking for sexual exploitation in the UK also rose by 11%, to 88.
The most common nationality or country of origin for child victims of trafficking (not just for sexual abuse) was Vietnam, followed by the UK and then Albania.
The figures come from the National Referral Mechanism (NRM), a government safeguarding framework which authorities and charities refer potential trafficking victims to.
The NCA said a total of 1,746 people from 112 different countries were highlighted as potential victims of trafficking in 2013 - up 47% on the previous year.
People were thought to have been trafficked for various reasons, including sexual exploitation and labour.
Nearly two thirds of those referred were female (1,122) and around a quarter (450) were children.
In total, the number of cases involving UK-born victims in 2013 rose 173% to 90; of those, 63 were children, an increase of 186% on 2012.
Liam Vernon, head of the NCA's UK human trafficking centre, said: "Increased awareness, both of human trafficking in its various forms and the obligation of first responders to use the National Referral Mechanism, is a likely contributor to the increased number of referrals in 2013.
"We know that this is a crime which affects some of society's most vulnerable people, and some victims will remain undetected. Equally, some of those referred to the NRM may not ultimately be classified as victims of human trafficking.
"The NCA is committed to relentlessly disrupting what is a criminal trade in human misery."
Home Office minister Karen Bradley said the figures were "unlikely to show the full scale of modern slavery nor the human suffering behind each statistic".
"The National Crime Agency is leading an enhanced and co-ordinated response to targeting trafficking gangs, we are increasing protection for victims, and we are strengthening legislation through a modern slavery bill," she added.
"The bill will send the strongest possible message to criminals that if you are involved in this disgusting trade in human beings, you will be arrested, you will be prosecuted and you will be locked up."
The NCA figures suggested there had also been a rise in the number of UK-born adults who were thought to have been victims of trafficking.
The 27 adults flagged up in 2013 represent a 145% increase compared with the previous year.
Albania was the most common nationality or country of origin for all referrals, followed by Nigeria and Vietnam.
There was a 53% rise (to 581 people) in potential trafficking for sexual exploitation for all the adult referrals.