TAIPEI, Aug 24 (Reuters) - Four people are missing after torrential rain lashed southern and eastern Taiwan on Monday, closing offices and schools, with ‌authorities bracing for a typhoon to hit the island later in ‌the week.

A low-pressure system has hovered over southern Taiwan for the past few days, bringing heavy ​rain and causing flooding.

The local governments of the two cities of Kaohsiung and Tainan, home to more than four million people, ordered offices and schools closed, as did the counties of Pingtung and Chiayi and the mountainous eastern counties of Taitung ‌and Hualien.

The Kaohsiung government said ⁠it expected cumulative rainfall over the five-day period of the low-pressure system to exceed 1.3 metres (4.3 feet), nearly half what ⁠the city typically expects in an entire year.

Taiwan's fire department said four people were missing in the floodwaters - three in Hualien and one in Tainan.

TSMC, the world's largest ​contract chipmaker, ​said in a statement it had completed ​routine heavy rain preparation procedures ‌at all its Taiwan factories, which were operating normally.

TSMC has factories in both Tainan and Kaohsiung, and is building new facilities in Chiayi country.

Taiwan Railway said there would be disruptions on the main east coast line and trains to and from Kaohsiung and Taitung with express services cancelled and local trains dependent on ‌weather conditions.

"If you've got nothing on, for ​goodness sake don't go out," Taitung county chief ​April Yao wrote on her Facebook ​page.

Taiwan's Central Weather Administration said separately that Typhoon Saudel, currently ‌heading towards Japan's southern Okinawa region, ​is expected to pass ​by the northern part of Taiwan early on Friday before reaching the eastern coast of China.

After passing the southern Japanese islands, it will slow ​and become a medium-strength ‌typhoon, though it is not forecast to make landfall on Taiwan ​but will bring heavy rain, the administration said.

(Reporting by Ben Blanchard; ​Editing by Lincoln Feast and Thomas Derpinghaus)