The Kaesong industrial complex in North Korea is reopening five months after it was closed due to political tensions with the South.
The BBC says a long line of trucks and cars began crossing the North Korean border at exactly 08:00 A.M today
More than 800 South Koreans are due to cross to the jointly-run centre.
Seoul has also sent negotiators who will discuss ways to attract foreign investment and ensure future stability.
The zone, just inside North Korea, is home to 123 South Korean factories that employ more than 50,000 North Koreans.
It is the last functioning inter-Korean joint project and a key source of revenue for Pyongyang.
The North removed all of its workers in April after its third nuclear test on 12 February sparked tensions on the Peninsula and led to expanded UN sanctions.
Shortly afterwards, South Korea and the US launched annual military drills, further angering Pyongyang.