SEOUL -- South Korea raised its typhoon-alert to its highest level on Monday as approaching Typhoon Hinnamnor forced flight cancellations, the suspension of some business operations and the closure of schools.

Heavy rain and strong wind pounded the south of the country as the typhoon approached from the south at a speed of 33 km per hour (20.5 mph). Hinnamnor is expected to make landfall southwest of the port city of Busan early on Tuesday, after reaching the holiday island of Jeju on Monday.

President Yoon Suk-yeol said he would be on emergency standby, a day after ordering authorities to do their best to minimise damage from the typhoon.

"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.

Hinnamnor is on a course that will take it northeast toward Sapporo, Japan, it said.

South Korea classifies typhoons in four categories – normal, strong, very strong, super strong. "Very strong" typhoons like Hinnamnor have wind speeds of up to 53 metres per second.

Warnings have been issued in the southern cities of Gwangju, Busan, Daegu and Ulsan, as well as on Jeju, while the Central Disaster and Safety Countermeasures Headquarters has upgraded its typhoon alert level to the highest in its four-tier system, for the first time in five years.

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

No casualties have been reported though more than 100 people have been evacuated and some facilities have been damaged by floods.

Shipbuilders Hyundai Heavy Industries, Daewoo Shipbuilding & Marine Engineering (DSME) and Samsung Heavy Industries said they would halt operations early on Tuesday.

A spokesperson for LG Electronics said it would halt operations on Tuesday at its Gumi production facilities that make large OLED TVs, while steelmaker POSCO is halting operations at its production facilities including its furnaces on Tuesday, the Yonhap news agency said.

SK Innovation, owner of South Korea’s top refiner SK Energy, said it asked carrier ships not to operate until the typhoon passes.

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.