BEIJING -- Typhoon Meranti triggered waves 17 meters high on Wednesday as it swept across seas off the southern coast of Taiwan, according to the National Marine Environmental Forecasting Center (NMEFC).

The waves were the highest ever recorded in the history of China's offshore wave surveillance, said the NMEFC, which on Wednesday upgraded its warning for ocean waves triggered by Typhoon Meranti to "red," the highest alert on a four-color warning system.

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

Meranti 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 has also advised that dams be reinforced.

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