Winds had weakened but forecasts said it would still pack the power of a Category 2 storm when it made landfall, possibly near Maoming, a big petrochemicals center.

The area has relatively few low-lying towns that would be vulnerable to storm surge as the typhoon makes landfall, and Guangdong, China’s most populous province, has extensive experience with typhoons, and makes elaborate preparations for each of them.

Evacuations of low-lying areas are mandatory. Fishing vessels are ordered into well-protected anchorages. After 16 workers were killed when their shanty collapsed in a typhoon in 2003, the province pursued a strenuous campaign of demolishing or upgrading substandard housing.

If Mangkhut shifts course slightly to the north, though, it could hit Hong Kong and the Pearl River Delta area, one of the world’s most important manufacturing hubs and home to more than 60 million people.

Hong Kong itself is quite resilient to typhoons. Although heavy rain may trigger landslides, the former British colony is not especially vulnerable to flooding because it has few low-lying areas.

The sprawling river delta around it, however, is barely above sea level and has struggled with flooding despite years of investment in drainage systems. Climate change has exacerbated the problem. The provincial capital, Guangzhou, has more to lose from rising seas and more severe storms than any other city on the planet, according to a World Bank report.