"The air quality of Beijing is definitely influenced by neighbouring provinces and ... we have made this air quality guarantee plan," Wang Jian, director of the division of Air and Noise Pollution Control at the State Environmental Protection Agency (SEPA), told Reuters in an interview.

"As long as this plan is carried out properly we will have no problem in meeting the standard of air quality for the Olympics and Paralympics."

Despite investing 120 billion yuan ($16.80 billion) on environmental improvement over the last decade, pollution is the biggest concern for Olympic organisers and athletes in the run-up to the Aug. 8-24 Games.

Olympic chief Jacques Rogge said last year that some endurance events might have to be rescheduled if air quality was poor.

More than 10 factories in Beijing and Hebei scheduled for closure over the next two years will now be shut down before June, Wang said.

The timed second stage of the plan involving the six provinces will start with the opening of the Olympic Village (July 27) and end when it closes after the Paralympics (Sept. 20), Wang said, without providing further details.

In the main emissions will be cut using air-cleaning technology or partial closures rather than the wholesale shutdown of industry.

"We took into consideration the endurance of the economy and we don't think it will have too big an impact on it," Wang said.

The plan, which is based on scientific studies at Tsinghua and Peking universities, starts with the worst polluters such as power and steel plants.

"It identifies polluters down to individual power plants and factories and says what they need to do and when they should start and finish their pollution reduction projects," he said.

Beijing's worst polluter, Shougang Steel, has already said it would move its facilities out of the capital by 2010 and reduce operations during Olympics -- part of raft of measures already in place in the capital.

The plan also recommended Beijing restricts the use of private vehicles by banning cars with registrations ending in odd and even numbers on alternate days, but the specifics of the measures would be down to the city authorities.

The scale of pollution reduction will also depend on climatic conditions in the capital during the Olympic and Paralympics, Wang said, with more restrictive measures being put in place if necessary.

"In the worst weather conditions, more reductions would be required of industry, more restrictions would be applied to vehicles and construction sites," he said.

"But scientists said the likelihood of the least helpful weather conditions in August is low."

(Additional reporting by Liu Zhen; Editing by Jeremy Laurence)