China gave foreign journalists rare access to a prison on Thursday in an attempt to show its progress in improving human rights ahead of the country's leadership change.

Rows of police officers greeted busloads of reporters on the eastern outskirts of Beijing before a limited and carefully controlled tour of the 1,000-person capacity No. 1 Detention Centre and its 200-bed hospital.

It is "very good to improve the transparency of our work so that the international community can see more clearly the actual situation here in China of public security supervision and law enforcement", said Zhao Chunguang, the director of detention supervision, in a welcome address.

Outside, the centre for pre-trial prisoners and convicts serving short sentences looked menacing with concrete walls, barbed wire and watchtowers. Inside it was spick-and-span and as brightly painted as a kindergarten.

One key element was missing, however: inmates.

Though journalists were advised not to take photos should they meet any, none were visible on the tour of the hospital or in the brightly painted cells, which included four beds and a bathroom separated by frosted glass, as well as an exercise area.

"It is a very good activity to invite foreign media friends to visit and interview in the public security supervision centres," added Zhao.

The tour -- organised amid a stream of state-run media reports about legal reforms, corruption crackdowns and welfare expansions -- fits into a wider effort to burnish the Communist Party's record before its power handover.

In a once-in-a-decade transition at the party Congress next month, a new set of leaders will replace President Hu Jintao and other top officials.

While some reforms have been undertaken in China, the No. 1 Detention Centre bore little resemblance to the cramped institutions described in rights reports that depict beatings as well as inadequate food, beds and medical aid.

Detainees are unable to meet lawyers, the reports say, while other offenders including dissidents disappear into unofficial "black jails" or are sentenced to "re-education through labour" by administrative panels.

Zhao ticked off improvements being implemented that were also outlined in a high-level white paper on judicial reform publicised this month -- and which were meant to be demonstrated during the tour.

No confessions should be extracted through torture, he said. Indeed, interrogation rooms featured floor-to-ceiling metal bars to keep questioners and detainees apart as well as security cameras trained on both.

The walls were covered in a special material to muffle sound, while the straight-back metal chair for detainees included a gleaming waist strap.

Another improvement showed off was the new standard of providing one bed per inmate, a change from the previous practice of squeezing as many as four onto an elongated mattress, an official explained.

Also on the tour were psychological counselling rooms, medical facilities like a pharmacy, X-ray and blood-test lab, and areas where detainees could meet family members and lawyers.

"The level of protection of detainee rights is a direct reflection of the level of protection of human rights in the country," Zhao said.

China will put into effect a new criminal procedure law in 2013 that, though widely criticised for endorsing secret detention centres, also strengthened certain rights such as detainees' access to lawyers.

Margaret Lewis, an expert in Chinese law at Seton Hall University in the United States, said parts of the law looked good on paper but the key was how the measures would be implemented.

"What is sorely needed now is not more reforms on paper but rather robust enforcement of suspect- and defendant-friendly reforms that are already in these laws," she said.

Lewis also stressed the need for an independent watchdog to monitor prisons. While "special inspectors" are meant to begin conducting random widespread visits, outside rights groups have generally not had such access.