BEIJING—The Chinese capital on Friday issued its second red alert for smog in two weeks even as unusually blue skies graced Beijing, illustrating leaders’ new efforts to predict severe pollution before it strikes.

The alert, which takes effect Saturday and runs through Tuesday, brings similar restrictions to those enforced earlier this month, which hobbled business activity across a swath of north China. Measures include school closures, restricted vehicle use, and shuttering factories and construction sites.

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