A parliamentary investigation into the Sewol ferry disaster got off to a shaky start Monday as only opposition party lawmakers visited the site of the shipwreck, with ruling party legislators absent from the trip.

Last week, family members of the victims demanded that lawmakers handling the investigation first visit them at Paengmok port on the southwestern island of Jindo to hear their voices on the disaster that left more than 300 people dead or missing.

All 18 lawmakers on the special parliamentary committee handling the probe were scheduled to visit the families Monday as their first activity for the 90-day investigation. The inquiry is aimed at determining the cause of the ferry Sewol's sinking on April 16.

Lawmakers of the ruling Saenuri Party, however, stayed behind, saying the family members had requested the committee members visit them another day.

"The waves are high, and all of the barges have retreated, while some of the family members are away receiving treatment for their injuries, so the families asked us to choose another date,"

Rep. Shim Jae-chul, a ruling party lawmaker and chairman of the committee, said in a press briefing at the National Assembly. "We didn't go because (the families) didn't want us to come."

The main opposition New Politics Alliance for Democracy claimed the ruling party had expressed its wish to postpone the visit due to scheduling issues of its own.

"They can't just say they can't go because they have other plans, without consulting us at all," Rep. Kim Hyun-mi, the opposition party leader of the committee, said. "The Saenuri Party planned this from the start in order not to go."

The parliamentary investigation comes as the exact cause of one of the nation's deadliest maritime disasters has yet to be determined.

An initial investigation by a joint police and prosecution team has shown that the tragedy was caused in part by cargo overloading and a failure to tie that cargo down properly.  (Yonhap)