She warned more than 20 police force areas were now aware of gangs “exporting” drugs to different regions across the country.
More than 600 people were arrested last week in connection with county lines gangs.
Jackie Sebire, a National Police Chief’s Council serious violence co-ordinator, told the committee she believed the amount of violence they were seeing was “a real peak”.
She highlighted an increase in much younger victims across the board and specifically more younger people being murdered.
The NCA says children aged between 15-17 make up the bulk of the vulnerable people involved in county lines, with both girls and boys being groomed and exploited.
Sebire added that even though “one victim is one too many”, serious violence was down by a third from the previous decade.
Iryna Pona, policy manager at The Children’s Society, described the findings as “shocking”.
She said: “Sadly come as no surprise to our practitioners, who encounter the cynical grooming of children as young as 11 by gangs to traffic drugs across the country.
“While children in care or growing up in poverty are often targeted, these perpetrators prey upon any sign of vulnerability, and this exploitation can affect any child in any community, causing unimaginable trauma.
“The progress outlined in this report in disrupting these gangs is welcome, but much more needs to be done to protect these children.”
In October 2018, a drug dealer was jailed for modern slavery offences after being found guilty of trafficking three teenagers from Birmingham in order to expand his drug network.
Zakaria Mohammed had been using county lines to force teenagers as young as 14 to sell drugs.