Typhoon Mitag is projected to arrive earlier than expected and make landfall on South Korea's southwest coast around midnight Wednesday, bringing heavy rains to the southern regions and Jeju Island from Tuesday.

The Korea Meteorological Administration said on Tuesday that Mitag, the 18th storm of the season, is currently moving northward after passing east of Taiwan.

The typhoon is forecast to pass the east coast of China and then veer east toward the Korean Peninsula before reaching South Korea's southwest coast.

The weather agency projects Mitag to move across the south of the country and exit to the East Sea on Thursday afternoon. 

The agency expects the tropical storm will bring torrential rains of 30 to 50 millimeters per hour to Jeju Island and eastern coastal areas on the peninsula from Tuesday to Friday.

Mountain areas in Jeju Island are forecast to receive up to 600 millimeters of rain during the period, while eastern parts of Gangwon Province and coastal areas in Gyeongsang Province are expected to receive 300 millimeters of rain.