China's Pearl River Delta, the country's manufacturing hub and home to tens of millions of people, is the world's most at-risk urban center from rising sea levels, according to a new study.

The region could be under at least 67 cm (26 inches) of water and as much as 2 meters by the year 2100 unless measures are taken now, according to Verisk Maplecroft, a U.K.-based risk advisory company.

Tokyo, Jakarta, Ho Chi Minh City and Shanghai, as well as Dubai, New York and Alexandria in Egypt are also in danger, according to the study, which assessed 500 cities with a population of more than a million.