Shares of TRIP.COM-S plummeted 18% on Thursday in Hong Kong trading after China's top business regulator initiated an investigation into the company.

China's State Administration for Market Regulations, or SAMR, began the investigation in accordance with the country's anti-monopoly law. The probe concerns suspected "abuse" of the company's dominance in the Chinese market, the regulator said.

Trip.com is cooperating with the probe and continuing operations as normal, the company said in a statement.

U.S.-listed depositary receipts of Trip.com fell 18% on Wednesday, putting the stock on pace for its largest single-day decline since Nov. 8, 2018, according to Dow Jones Market Data. Shares listed in Hong Kong closed Wednesday down 6.5%.

The company, which has headquarters in both Shanghai and Singapore, owns booking sites and travel agencies like Ctrip, Skyscanner, and the eponymous Trip.com. Ctrip has sometimes been referred to as "China's Expedia," owing to its widespread use by Chinese travelers.

The investigation comes just a month before Lunar New Year, which is a popular travel period in China.