|Sunday's pollution, bottom right, capped a week of smog-filled skies and was said to be the worst seen in the past month [Reuters]
Less than two weeks before the opening of the Olympic games, Beijing continued to be shrouded in smog on Monday as officials considered further emergency restrictions to try to clear the air.
Humid weather conditions and low winds have meant efforts to clear the city's notoriously polluted skies have so far had only patchy results at best.
Pollution is one of the biggest question marks hanging over the games which are due to open on August 8.
On Sunday a ceremony to open the athletes' village was overshadowed by a pall of pollution said to be the worst seen in the past month.
Around the Olympic Green area, the centrepiece for the games, visibility was reduced to about 1km.
That was despite a raft of special restrictions introduced in the past week that have shut factories, halted construction work and cut the number of vehicles on the capital's roads by half.
On Monday state media reported that further emergency measures could be applied if the air quality did not improve sufficiently.
That could mean a tightening of restrictions on vehicle use that could mean up to 90 per cent of private vehicles being banned from using the city's streets at any one time during the games.
|The city may take more vehicles off the roads [GALLO/GETTY]
At present vehicles with odd or even licence plates may use the capital's roads on alternate days, in effect allowing only half the city's 3.3 million vehicles to hit the roads on a given day.
The smog is created by a combination of temperatures around 32C, with 70 per cent humidity and low winds, which turns the city's air into a soupy mix of harmful chemicals, particulate matter and water vapour.
The Beijing Municipal Environmental Protection Bureau said the air was "unhealthy for sensitive groups".
Du Shaozhong, the bureau's deputy director, blamed the continued haze on a combination of fog and light winds that were unable to blow away the pollution.
"Our job is to decrease the pollution as much as possible, but sometimes it is very common to have fog in Beijing at this time," he said.
"The air quality in August will be good."
City officials have promised clear air for the duration of the Olympics which the government sees as a showcase event and the country has spent billions of dollars on efforts to clean up the capital's environment.
This week is expected to see a surge in the number of athletes arriving in Beijing ahead of the games.
However, several teams have opted to base themselves outside of China in nearby Asian countries in an effort to avoid Beijing's air for as long as possible.
Some delegations, including the US Olympic Committee, have made protective facemasks available to their athletes.