Beijing issued an orange alert for severe air pollution Friday, the second-highest on the city’s four- grade scale, warning children and the elderly to avoid outdoor activities.

The concentration of PM2.5 -- the particles that pose the greatest health risks -- was 553 micrograms per cubic meter near Beijing’s Tiananmen Square at 10 a.m. after reaching 647 in the early morning, according to the municipal air-monitoring website. The World Health Organization recommends PM2.5 exposure of no more than 25 over 24-hours.

The lasting air pollution has renewed calls for the government to make better forecasts and take faster action to counter the issue. The Chinese capital this year has imposed two red alerts, the highest on the scale, prompting measures including school closures, traffic restrictions and factory operation limits. The latest ended on Tuesday.

Smog also blanketed China’s eastern and central regions. PM2.5 levels were as high as 379 micrograms per cubic meter in both Zibo and Jinan of Shandong province, data from the China National Environment Monitoring Center showed. The readings were 389 in Wuhan and 338 in Huanggang of Hubei province.

Shanghai issued a yellow alert Friday for air pollution, the third-highest of four levels. Children and the elderly were warned to avoid outdoor activities, with the Shanghai Environmental Monitoring Center reporting PM2.5 levels of 114.9 micrograms as of 9 a.m.

About 50 cities in northern and eastern China have issued air pollution alerts, the China Daily reported on Friday. Smog across the eastern, northern and central parts of the country will weaken or disperse from north to south from Saturday, the China Meteorological Administration said.