ST. CLOUD — Sex trafficking at illicit massage businesses in central Minnesota is increasing at an alarming rate, according to county officials.

A Waite Park business police raided earlier this month is one of at least seven in the area regularly advertising on websites known for selling sex, the St. Cloud Times reported . Riverwood Massage and Body Works owner Yanhang Lin was charged with sex trafficking and promoting prostitution. Jail records don’t list an attorney for her.

Minnesota is one of four states that don’t regulate massage therapy at a statewide level, officials said. Local governments are responsible for regulation, which can create loopholes for traffickers.

There are about 40 licensed massage businesses in Waite Park and St. Cloud. While most operate legitimate businesses, some “are a front for sexual activity,” Waite Park Police Chief Dave Bentrud said.

“It’s just an ongoing battle to deal with sex trafficking,” Bentrud said. “The demand is still there.”

There were more than 360 human trafficking-related convictions in Minnesota in 2016, up from 275 in 2014, according to a report released last year by the state Office of Justice Programs and the state Statistical Analysis Center.

The numbers don’t fully illustrate the extent of trafficking because most individuals involved in human trafficking aren’t arrested, charged or convicted, the report said. Sex trafficking is also often connected to international networks, authorities said.

The Central Minnesota Human Trafficking Task Force was formed in March to address the issue. The partnership involves organizations from Stearns County, St. Cloud, Waite Park and the Central Minnesota Sexual Assault Center.

A Minnesota Office of Justice Programs grant helped fund the official creation of the task force. The task force includes a full-time investigator from the Waite Park Police Department and the St. Cloud Police Department. Stearns County has a part-time investigator and a data analyst is also a part of the team.