(CNN) -- Texas authorities are investigating "the safety of children" at a ranch occupied by about 400 followers of polygamist sect leader Warren Jeffs, officials said Friday.



An aerial view taken last year shows some living quarters at polygamist leader Warren Jeffs' Texas ranch.



Authorities have sealed off the 1,900-acre ranch near Eldorado and no one is allowed to enter or leave, officials with Child Protective Services and the Department of Public Safety said.



The people living at the ranch are cooperating, authorities said.



Escorted by police, social workers entered the compound in south central Texas at 8 p.m. Thursday after receiving "a referral," said Child Protective Services spokeswoman Marleigh Meisner.  Watch police seal off the compound »



Child Protective Services "is conducting an investigation into safety issues of the children who live within the compound," she said.



Meisner would not provide details about the referral but did say officials responded "within days" of receiving it. As of Friday morning, Meisner added, her agency had "not determined that there is a safety issue with these children."



Several law enforcement agencies are assisting with the investigation, said Tela Mange, of the Texas Department of Public Safety. "The people at the ranch have been cooperative and they are providing the investigators with everyone they want to talk to," she said.



Jeffs' Fundamentalist Church of Jesus Christ of Latter Day Saints (FLDS) bought 1,900 acres near Eldorado four years ago and built the ranch, which they call the YFZ Ranch. It is now home to as many as 400 members who relocated from their Arizona and Utah compounds.



Jeffs, the 52-year-old leader and "prophet" of the 10,000-member church, was convicted in Utah last year on two counts of being an accomplice to rape, charges related to a marriage he performed in 2001. He still faces trial in Arizona on eight charges of sexual conduct with a minor, incest and conspiracy.



State and local law enforcement agencies set up roadblocks around the ranch Thursday evening, preventing journalists from seeing what was happening on the property, according to Randy Mankin, editor of the Eldorado Success weekly newspaper.



"This came totally out of the blue," Mankin said.



There were no indications of any violence around the ranch, he said.



When CNN crews have visited the ranch, it was guarded by armed men equipped with night vision gear and other high-tech surveillance tools to prevent intruders.



When CNN flew over the ranch in a small plane last year, the crew saw a massive temple, the three-story housing units where Jeffs' chosen followers live, the water tower, the school and community center, the dairy and cheese factory and a massive concrete mill.



The FLDS church openly practices polygamy in two towns straddling the Arizona-Utah state line -- Hildale, Utah, and Colorado City, Arizona., but members living on their Texas ranch rarely venture into Eldorado, four miles to the south.



Critics of the sect say it arranges marriages for girls as young as 13, and that competition for brides may be reduced through exiling young men. If male followers are excommunicated, the critics claim, their wives and children can be reassigned to someone else.



Jeffs is now being held in the Mohave County Jail in Kingman, Arizona, where he will be tried on charges of being an accomplice to incest and sex with minors.



In November ,Jeffs was sentenced to 10 years in jail after being convicted of two charges of accomplice to rape. E-mail to a friend
When was Jeffs put in jail? What charges did Jeffs face? who is interviewing? where is jeffs What state's agents were interviewing the children? where is the compound who is not permitted? who are awaiting trial? who is talking to the children
last year sexual conduct with a minor, incest and conspiracy. authorities Mohave County Jail in Kingman, Arizona, Texas near Eldorado no one is allowed to enter or leave, Warren Jeffs, Child Protective Services
question: When was Jeffs put in jail?, answer: last year | question: What charges did Jeffs face?, answer: sexual conduct with a minor, incest and conspiracy. | question: who is interviewing?, answer: authorities | question: where is jeffs, answer: Mohave County Jail in Kingman, Arizona, | question: What state's agents were interviewing the children?, answer: Texas | question: where is the compound, answer: near Eldorado | question: who is not permitted?, answer: no one is allowed to enter or leave, | question: who are awaiting trial?, answer: Warren Jeffs, | question: who is talking to the children, answer: Child Protective Services