Also this weekend, police will start checking Beijing subway passengers for guns and explosives, the reports said.
The measures reflect the fears of Chinese leaders, who worry the Olympics might be tarnished by security threats. They also hope to stop activists who want to use the August games to air grievances against the communist government.
At the airport, two-member teams of guards with machine guns began work Thursday and will patrol all three terminals through the end of the Olympics, the Xinhua News Agency and newspapers reported. Chinese police usually are unarmed, while some airport guards carry pistols.
"I think they look cool, and you rarely get to see such big guns," the China Daily newspaper quoted a female traveler at the airport as saying.
On subways, police with dogs will start checking passengers for guns, knives, explosives and flammable, poisonous or radioactive material on Sunday, Xinhua said.
The checks are to last through the Aug. 8-24 Olympics and the Sept. 6-17 Paralympics, the agency said.
"Passengers who reject security checks or insist on carrying dangerous articles will be banned entry or exit and even punished by law," a spokesman for the subway was quoted as saying.
China's post office has suspended carrying parcels containing chemicals or liquids through Oct. 31.
