South Korean companies operating in the joint industrial complex in the North are required to change their work hours according to Pyongyang's new time zone, Seoul officials said Sunday.

North Korea told the Ministry of Unification in Seoul on Saturday that it will start handling entries into the Gaeseong Industrial Complex in accordance to its new standard time, which is now 30 minutes behind that of South Korea, a ministry official said.

Earlier this month, Pyongyang said it is rolling back its time zone, set by Japan during its 1910-45 colonial rule over the Korean Peninsula, to mark the 70th anniversary of liberation this year.  

Saturday's announcement effectively pushed back all planned entries by South Korean businessmen into the complex by half an hour, which means South Koreans working there will have to start and finish work later than normal.

Starting Monday, South Koreans can enter Gaeseong no earlier than 9 a.m. and can leave no later than 5:30 p.m., the ministry official said.

"We will take all necessary measures to ensure a smooth transition to the new entry system," the official said.

South and North Korea had been using identical standard times.

A total of 124 South Korean small and medium enterprises operate production facilities at the park, which opened in 2004 and remains the most salient outcome of inter-Korean rapprochement. (Yonhap)