Typhoon Omais reached close to South Korea's southern resort island of Jeju on Monday, bringing heavy rains and strong winds, the weather agency said.

The typhoon, packing a maximum wind speed of 25.3 meters per second, arrived near Seogwipo city of Jeju at around 7:40 p.m., and was travelling northeastward, according to the Korea Meteorological Administration (KMA).

It is forecast to be downgraded to an extratropical cyclone after midnight, but continue to bring heavy downpours and strong winds up in the southern regions until Tuesday afternoon, the agency said.

A typhoon warning was issued for the entire island and nearby seas Monday afternoon, and major cities and provinces, including the southern city of Busan and the Gyeonggi Province, issued landslide warnings.

The Busan city is also projected to see heavy rain of 70 mm per hour and 30 meter-per-second wind gusts, with some areas receiving as much as 400 mm of rain until Tuesday.

The government of the southeastern city of Changwon ordered residents in its 73 areas prone to landslides and flooding to evacuate.

South Jeolla Province also said it will evacuate 12,000 residents living in some 4,000 areas to sturdier places in advance, while cordoning off some public areas, such as underground parking lots, that are susceptible to flash flooding. The province is forecast to receive heavy rainfall of up to 400 mm.

The southwestern port city of Yeosu is bracing for the impact of the typhoon, closing down makeshift testing centers for COVID-19 and anchoring boats and seaside structures.

Most southern parts of the country are under heavy rain watch, which is issued when more than 60 mm of rain is forecast for a span of three hours.

The weather service warned strong winds and a storm surge could disrupt public transportation to the island until Tuesday, and advised the local governments, and especially residents in low-lying areas, to thoroughly prepare for the storm.

As of 6:30 p.m, 75 flights to and from the island were grounded as a wind gust warning was issued on the island around noon, according to the Korea Airport Corp.

Most fishing boats and eight ferries connecting Jeju and other ports, including Mokpo and Busan, were canceled due to high winds. (Yonhap)