By Louisa Lim
BBC News, Beijing
Mr Nowak will spend nearly two weeks in China
The UN rapporteur on torture, Manfred Nowak, has arrived in China for a fact-finding mission to examine allegations of official maltreatment.
It is the first time a UN rapporteur on torture will be allowed to visit China's prisons and detention centres.
It has taken years of negotiations for Beijing to agree to the trip.
Mr Nowak's visit comes at a time when a public debate is going on in the Chinese media about the use of torture and coercion by the police.
Mr Nowak will spend almost two weeks in the country, travelling to Tibet and the restive far western region of Xinjiang.
Beijing outlawed torture in 1996, but activists say it is still widely practised.
In fact, there has been an outcry in recent months about police brutality and torture, after a number of cases came to light showing how police coerced false confessions.
In one case, a man who had been sent to prison for murdering his wife was released after she was found alive.
He had been tortured into confessing to the murder, and he had already served 11 years of his sentence.