South Korean firms summoned by North Korea for a probe into their real estate holdings at the North's Mount Geumgang district left for the North early Thursday morning.

Sixteen officials from Hyundai Asan and its seven partner firms boarded a bus headed for Mount Geumgang at Hyundai Asan headquarters in Seoul at 5 a.m.

The partner firms are expected to begin their meeting with the North at 11 a.m. and will return to Seoul around 4 p.m.

The firms will, however, visit once more for a two-day trip before next Wednesday for further inquiries.

The association of firms for the tour program to Geumgang says that the summons was a unilateral demand made by the North and that they will know more about the North’s motives behind the call for the probe after the Thursday meeting.

Three officials from the Korea Tourism Organization, which owns a pavilion at Geumgang, went to the North on Wednesday as part of the probe.