China tightened a wide-ranging clampdown on dissidents and blocked some news websites Friday, hours ahead of the awarding of the Nobel Peace Prize to imprisoned democracy activist Liu Xiaobo.

Uniformed and plainclothes officers guarded the entrance to the compound in central Beijing where Liu's wife, Liu Xia, has lived under house arrest since the October announcement that her husband would receive the prize.

BBC and CNN went dark in China after both stations switched to live coverage as the ceremony began in Oslo. Several dozen journalists at Liu's home were herded away by police to a cordoned-off area.

For weeks Liu has been prevented from leaving, receiving visitors or communicating with the outside world, but security was visibly tighter Friday. Police cars were positioned on every surrounding corner and officers patrolled outside the apartment block. There was no sign of life at the apartment windows.

Guards checked the identities of all who entered, while about a dozen journalists stood just outside the gate keeping watch.

Liu Xia's phone and Internet connections have been cut off, and friends, family and colleagues in the country's embattled dissident community have been placed under house arrest or tight surveillance. Several in the community, including renowned artist Ai Weiwei and human rights lawyer Mo Shaoping, have been barred from leaving the country, apparently out of fear they might attend Friday's award ceremony in Norway's capital.

The imprisoned Liu will be represented by an empty chair in Oslo, and because no one close to him can receive it, the award will not be handed out for the first time since the 1930s.

As part of the widening clampdown, Beijing police in recent days have emptied apartments, hustling many activists away from the capital to keep them out of the loop entirely.

Before being escorted to the southwestern province of Yunnan, Zhang Xianliang, the mother of a high school student killed in the 1989 Tiananmen Square crackdown on pro-democracy demonstrators, told The Associated Press she had been shadowed by four plainclothes agents who incessantly demanded she leave Beijing.

"They have become crazy. This is unprecedented. I have never been so threatened in the last 20 years," Zhang said.

Activist lawyer Jiang Tianyong said he managed to evade security agents. "We will be unable to watch the ceremony today, unable to see Liu Xiaobo or his wife Liu Xia picking up the award. But no matter what, history always goes forward and there will still be people celebrating this great historical moment," he said in a Skype interview.

Websites of foreign news outlets were blocked and earlier broadcasts by CNN and the BBC were blacked out when reports about Liu were shown.

Liu's award has elicited a furious response from Beijing, with daily tirades in state media berating the Norwegian Nobel Committee as misguided and inherently opposed to China's development. Foreign Ministry spokeswoman Jiang Yu this week described Liu's supporters as "clowns," and accused the committee of "orchestrating an anti-China farce by themselves."

China has suspended trade talks with Norway in retaliation and pressured foreign nations not to attend the award ceremony. China and 17 other countries — mostly fellow authoritarian states — have declined invitations to attend the event.

The vilification campaign has rocketed Liu from relative obscurity to worldwide fame despite the communist leadership's desire to negate his influence with an 11-year prison sentence for sedition. The term — Liu's fourth period of incarceration since 1989 — was handed down after he co-authored a bold appeal for human rights and multiparty democracy known as Charter 08.

Security was also tightened Friday on Beijing university campuses: Additional guards were posted and visitors required to show identification on entering.

While many students expressed support for Liu's democratic ideals, some backed the government's depiction of him as a source of conflict and unworthy of such an honor.

"The prize has become so political," said Peking University student Grace Lee. "It's supposed to be for people who struggle for peace, not people who cause conflict between countries."