Typhoon Hinnamnor neared South Korea on Monday, forcing flight cancellations, suspensions of some business operations and closures of schools, as the country raised its typhoon-alert level to its highest.

Heavy rain and strong wind pounded the southern part of the country, with the typhoon travelling northward at a speed of 24 km per hour (15 mph). Hinnamnor is expected to make landfall southwest of the port city of Busan early on Tuesday, after reaching waters off Jeju Island later on Monday.

President Yoon Suk-yeol said on Monday he will be on emergency standby, a day after ordering authorities to put all efforts into minimising damage from the typhoon that has been classified as "very strong".

"Very strong winds and heavy rains are expected across the country through to Tuesday due to the typhoon, with very high waves expected in the coastal region along with storm and tsunami," the Korea Meteorological Administration (KMA) said.

According to KMA's forecast, Hinnamnor is headed northeast toward Sapporo, Japan.

South Korea classifies typhoons in four categories - normal, strong, very strong, super strong - and Hinnamnor is expected to reach the country as a "very strong" typhoon, according to the KMA. Typhoons under that classification have wind speeds of up to 53 metres per second.

Warnings have been issued across the southern cities, including Gwangju, Busan, Daegu and Ulsan, following that in the southern island of Jeju, while the Central Disaster and Safety Countermeasures Headquarters on Sunday upgraded its typhoon alert level to the highest in its four-tier system, the first time in five years.

Busan city and its neighbouring areas have received rain throughout the weekend, with more rain forecast across the wider country for Monday and Tuesday.

No casualties have been reported so far, though more than 100 people have been evacuated and at least 11 facilities have been damaged by floods.

Steelmaker POSCO told Reuters it is considering suspending some of its production processes in the city of Pohang on Tuesday, while SK Innovation, owner of South Korea's top refiner SK Energy, said it asked carrier ships not to operate until the typhoon passes.

Responding to local media reports over the planned halts of their operations, South Korean shipbuilders Korea Shipbuilding & Offshore Engineering, Daewoo Shipbuilding & Marine Engineering (DSME) and Samsung Heavy Industries, DSME said a decision on suspending its operations will be made later on Monday.

Korean Air Lines and Asiana Airlines have cancelled most of their Monday flights to Jeju Island, according to their websites, while budget airlines such as Air Seoul and Jin Air have cancelled some of their flights.