BEIJING (AP) — Chinese weather forecasters and state media say the dense, gray smog that has smothered much of China, closing schools and grounding planes, may finally soon give way.

The national weather authority said Wednesday that nighttime winds will push out much of the air pollution that has left Beijing and dozens of other cities under a five-day "red alert," the highest level in China's four-tiered warning system.

By the calculations of Greenpeace East Asia, the red alert affects 460 million people. Authorities have closed schools, grounded hundreds of flights and announced emergency shutdowns of factories and highways.

Still, Beijing's air pollution readings on Wednesday remained 15 times above the level considered safe by the World Health Organization. Readings in some cities outside the capital were even higher.