Here are some facts about security at the Games which open on Friday.

SCREENING VISITORS, LOCALS

-- Visa rules have tightened. Travelers must now show a return air ticket and a hotel booking before buying a visa.

-- Hong Kong, host of equestrian events, has created a watchlist of unwelcome activists and brought in new visa restrictions.

-- Interpol is to give Beijing airport and other major border entry points access to its database of more than 14 million lost or stolen travel documents.

-- Many Beijing dissidents and their families are being held under house arrest. Petitioners who have come to the capital to present complaints have often been detained, they said.

SECURITY CAPABILITIES

-- A 100,000-strong security force, including the elite Snow Wolf Commando Unit, is on alert.

-- 300,000 surveillance cameras watch the city.

-- Since May, the team of People's Liberation Army (PLA) engineers in charge of Games security checks and emergency rescues has run daily drills on finding and defusing explosives and rescuing and evacuating people from damaged buildings.

-- The U.N. nuclear watchdog has trained Chinese security personnel in how to respond to radiological attacks -- such as a "dirty bomb" -- in which radioactive material is released.

OLYMPIC VENUES

-- At least two surface-to-air missile launchers were set up in late June south of the Bird's Nest National Stadium.

-- Authorities pledged to revamp public emergency shelters by the venues last October, saying 20 to 30 new shelters, with room for 1.5 million to 2 million people, were needed every year.

-- Gas stations within 300 meters of Olympic venues and all Games-designated gas stations must install video surveillance equipment and "explosion-prevention devices".

-- Unmanned spy planes will fly over the east coast city of Qingdao, host of sailing events.

BEIJING CITY

-- Random identity card and passport checks have increased.

-- On Friday, Tiananmen Square was closed and surrounding streets cleared of people, many of them Chinese tourists.

-- Security checks are in place on public transport, with spot checks on bottled drinks, and x-ray machines and sniffer dogs deployed in subway stations to check luggage.

-- Liquids, matches and lighters have been banned in hand luggage on domestic flights since officials said crew foiled an attempted airline bombing in restive Xinjiang province in March.

-- Fireworks have been banned from the Chinese capital for three months from July 1; and some bars and restaurants close to Olympics venues have been told to shut down. Kites and homing pigeons have been banned from seven districts to clear airspace.

-- To prevent food safety problems or sabotage, inspectors will be posted in factories making food for the Olympics.

RESTIVE REGIONS

-- With authorities keen to present China as a harmonious nation, rights groups say restive western regions of Tibet and Xinjiang have seen controls tightened.

-- Deadly riots in Tibet in March, and in southwest Weng'an county, Guizhou, in late June, have highlighted social strains and prompted a new stability drive.

-- Local officials have been ordered to defuse petition campaigns by discontented citizens to prevent "mass incidents" such as riots and demonstrations.

Sources: Reuters, Chinese media

(Writing by Gillian Murdoch, Beijing Editorial Reference Unit; Editing by Nick Macfie)

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