HAIKOU/GUANGZHOU, Sept. 15 -- Thousands of fishing vessels have returned to harbor as authorities in south China issued a top alert for typhoon Kalmaegi.

Nearly 26,000 fishing boats returned to shore in the island province of Hainan, said Chen Wu, spokesman for the provincial flood control headquarters on Monday.

The Hainan government issued the highest Grade I alert at 10 a.m. Monday for Kalmaegi, which was spotted on the sea 645 km southeast of Leizhou City, Guangdong Province at 4 p.m. Monday.

The storm is moving at a speed of 30 km per hour northwestward and packing winds of up to 137 km per hour, said the National Meteorological Center.

Schools, government units who have no work related to typhoon prevention, and enterprises, will have Tuesday off in Haikou, the provincial capital.

Shipping services and passenger trains on the Qiongzhou Strait, which connects Hainan and Guangdong, were suspended at 1 p.m. Monday.

Flood control authorities in Haikou advised the public to reduce outdoor activities as much as possible.

Guangdong also launched a top level response to the typhoon, which is forecast to land somewhere between Wuchuan in Guangdong and Wanning in Hainan between Tuesday morning and midday.