The restart is seen as the most substantial sign of warming relations between the two sides following tensions earlier this year over Pyongyang’s missile and nuclear tests.  

Lines of trucks and cars crossed South Korea's northern border checkpoint Monday morning on the way to Kaesong, North Korea.
 
About 800 South Korean managers and their staff entered the suspended, jointly run factory zone at Kaesong with materials and parts to restart production for the first time in months.