Thick smog is choking Beijing and much of north China, as the worst period of air pollution this year stretches into a fifth day.
Beijing issued an orange-level pollution alert this weekend, its highest of the year. Residents are advised to stay indoors. The city's monitoring center reports that concentrations of PM2.5, tiny airborne particles that embed deeply in the lungs, peaked at 900 micrograms per cubic meter in southern Beijing as of Monday.
Municipal education authorities advise students in middle schools and high schools stop outdoor activities. Some schools have suspended class temporarily. The severe pollution is expected to last until a cold front arrives later today.