Mexican officials said they had arrested former US university professor Walter Lee Williams, an alleged child sexual predator on the FBI's list of top 10 Most Wanted criminals.

Williams was arrested in Playa del Carmen, a seaside resort town just south of Cancun on Mexico's Caribbean coast, said Gaspar Armando Garcia, the Quintana Roo state prosecutor.

Williams is considered "extremely dangerous" and is being closely guarded, Garcia said.

The US Federal Bureau of Investigations put Williams, 69, on its Top Ten list on Monday. A federal arrest warrant was issued against him on April 30 on charges of exploiting minors.

"Because of his status he has the means and access to children, and that's what makes him dangerous," Special Agent Jeff Yesensky said in an FBI video on Williams. "He preys on the most vulnerable children."

The FBI was offering a reward of up to $100,000 for information leading to his arrest.

Garcia said that Williams was arrested late Tuesday in a public park at 8:30 pm local time (0130 GMT Wednesday), and upon questioning "could not prove" that he was legally staying in the country.

Williams was formerly a tenured professor at the prestigious University of Southern California, according to the Los Angeles Times, and was a specialist in anthropology and gender studies.

According to the FBI video, Williams's victims "are boys between the ages of 14 and 17, many of whom live in Third World countries."

Williams has traveled extensively throughout southeast Asia, including Indonesia and the Philippines, as well as Mexico and Peru, the FBI said.