The new emergency measures include shutting another 200-plus factories and further restricting vehicles across Beijing, Tianjin city and surrounding Hebei province, according to a notice posted Thursday on the government's Web site.
In Beijing, besides current restrictions banning odd/even license plates on alternate days, automobiles whose last digit matches the last digit of the date would be banned.
Tianjin and Hebei would begin implementing similar odd/even restrictions.
In addition, all construction sites across Beijing would be halted.
The notice said once the games begin Aug. 8, the contingency measures would kick in if authorities decide the air quality had not improved enough.
"If there are unfavorable weather conditions, and the air quality is forecast to not to meet the standards in the following 48 hours, the operating commanding center would suggest the contingency plans be initiated," it said.
On Thursday, the pollution index rose up to 69, but remained within the national standard for acceptable air.
A day earlier, the city's air pollution index had dropped to 44, less than half what it was on Tuesday, and the lowest since July 20 when the first measures came into effect.
A cooling wind and some rain earlier this week helped sweep away pollutants and gave Beijingers a respite from the sultry heat and humidity that had cloaked the city for days.
A reading below 50 is considered good and between 51 to 100 is moderate. But critics say even moderate levels are still above the World Health Organization's guidelines for healthy air.
Some experts argue that the recent weather conditions, not the curbs, were largely responsible for the cleaner air.
Athletes participating in the Aug. 8-24 games have raised concerns about the impact of the city's pollution on their health and their performance from the start.
Some of the 10,500 Olympic athletes began arriving in large numbers this week
-- though others headed to train in neighboring South Korea, Japan and other places to avoid Beijing's air for as long as possible.