BEIJING -- China's National Marine Environmental Forecasting Center (NMEFC) on Wednesday upgraded its warning for ocean waves triggered by Typhoon Meranti to "red," the highest of a four-color warning system.

Gales and monster waves up to 12-meters high have been observed off the eastern coast of Taiwan, as this year's 14th typhoon is moving westward, and surges are expected off the coast of Fujian, Zhejiang and Guangdong provinces on Wednesday and Thursday.

The typhoon is expected to make landfall in Fujian and Guangdong on Thursday and the State Oceanic Administration has initiated a class-II emergency response, the second highest level.

The NMEFC ordered ships to return to harbor and residents to stay indoors. It also advised that dams be reinforced.

China's four-tier warning system for severe weather features red as the most serious, followed by orange, yellow and blue.