SHANGHAI (REUTERS) - China's northern regions are facing a sustained period of pollution for at least the next two weeks, the environment ministry warned, with heavy smog threatening to overshadow the country's National Day celebrations in Beijing in October.

China will mark the 70th anniversary of the founding of the People's Republic on Oct 1, with Beijing and the surrounding province of Hebei already implementing special measures to tighten security, curb firework sales and suspend mining activities in order to minimise potential disruptions.

Cities throughout the region have also imposed routine output curbs on steel mills, power plants, coking coal producers and cement factories in the final week of September, triggered by declining air quality.

But the Ministry of Ecology and Environment said in a statement published late on Monday (Sept 23) that prolonged and adverse weather conditions across eastern coastal regions were still expected to lead to heavy smog build-ups in and around Beijing over the next two weeks.

It said low pressure east of the Taihang mountain range between the provinces of Hebei and Henan would allow emissions to be pushed north to Beijing, where high humidity levels would speed up the conversion of industrial and vehicle emissions into damaging airborne smog particles.

It said it had notified local governments in the cities of Beijing and Tianjin as well as the provinces of Hebei, Shanxi, Shandong, Henan, Anhui and Jiangsu, urging them to pay close attention to smog and take action where appropriate to reduce emissions.

Tangshan, China's biggest steelmaking city, is already stepping up efforts.

It issued an orange smog alert on Monday and imposed stricter curbs on blast furnaces and electric arc furnaces at steel mills from Tuesday, according to a document reviewed by Reuters and confirmed by a source with a local steel association.

Other cities in Hebei, including Hengshui and Cangzhou, also issued anti-pollution curbs starting from Sept 24 following orders from the provincial environmental regulator, according to statements from local government and state media.

China has often blamed pollution on unfavourable weather, including weak wind speeds, humidity and high temperatures.

But the environment ministry has also criticised local governments for using weather as an excuse for their poor performances when it comes to tackling pollution.