TORONTO -- A Canadian man facing charges in the U.S. over an alleged reptile smuggling operation was caught at the border with 51 live turtles stuffed down his pants, recently unsealed court documents say.

The U.S. federal court documents say officers with the Canada Border Services Agency intercepted Kai Xu as he attempted to cross into Windsor, Ont., from Detroit last month.

"During the secondary inspection, Xu was found to have 51 live turtles tapped (sic) to his person," Kenneth Adams, a special agent with U.S. Fish and Wildlife Service, stated in an affidavit outlining the criminal complaint.

"Specifically, Xu had 41 turtles tapped (sic) to his legs and 10 hidden between his legs."

Canadian authorities seized the turtles, which included North American varieties such as eastern box turtles, red-eared sliders and diamondback terrapins -- some of which sell for $800 each -- and turned them over to American officials.

While the interception occurred in August, details were only made public after Xu and a second Canadian, Lihua Lin, 30, of the Toronto area, were arrested and charged in U.S. district court this week following an investigation by the Fish and Wildlife Service.

Xu, 26, and Lin appeared in federal court in Detroit on Thursday charged with smuggling, illegal trading and exporting. They could face up to 10 years in prison if convicted.

In a separate criminal complaint against Xu's co-accused filed with the court, Special Agent Matthew Martin described how wildlife officials witnessed "known reptile smuggler" Xu pick up several boxes of live turtles in Novi, northwest of Detroit, on Tuesday.

The document said he then drove to a hotel near the Detroit international airport, where he placed the reptiles in a room he had booked for two nights, later meeting up with Lin at the hotel.

On Wednesday, the document said, Xu dropped Lin off at the airport bound for Shanghai, China. Lin, who checked in two pieces of luggage, was arrested after a search turned up more than 200 North American pond turtles.

None of the allegations has been proven in court and the accused have not offered a defence.

The turtles are apparently prized as food or pets in China.

In his detailed complaint, Adams described how his agency had received a tip Aug. 5 from a courier company in Detroit about a parcel addressed to Xu that was awaiting pickup.

The brown box, which had been shipped from Alabama, weighed about three kilograms and had no air holes but carried the notation "Live fish -- keep cool."

On the same day, U.S. border agents notified the fish and wildlife agency that Xu had crossed into Detroit from Windsor in an SUV.

Adams and other agents then staked out the courier depot, where Xu arrived to pick up the brown parcel.

The complaint states Xu then apparently opened various boxes in the rear of the SUV, took out several round clear plastic containers, and placed their contents into plastic baggies, and was also seen with packaging tape and scissors.

"Xu turned towards me as he looked around the parking lot," Adams states.

"As he did so, Special Agent (James) Fuller noticed irregularly shaped bulges under Xu's sweatpants on both his legs."

Xu then drove toward Windsor, where he was stopped.

He is due to appear in bail court in Detroit on Friday, said Gina Balaya, a spokeswoman with the U.S. attorney's office.

Lin was released on US$10,000 bail. Conditions include having no contact with Xu and entering the U.S. only for court.