Two cranes collided at the shipyard in the southeastern port of Geoje, causing a 60-metre, 32-tonne crane section to break and crash onto a workers' rest area below.
Six people were killed and 25 injured in what police described as "chaotic" scenes on Monday.
All those involved were working on the Total project, which was ordered in December 2012 and is destined for its Martin Linge field off Norway.
The shipyard is operated by Samsung Heavy Industries, part of the sprawling Samsung Group, South Korea's largest conglomerate.
Park Dae-Young, president of Samsung Heavy Industries, said he "sincerely apologised" to the victims and their families and promised to provide full support to those affected.
"We will thoroughly investigate the cause of the accident and take responsibility," Park said in a statement read out by Kim Hyo-Seop, head of the Geoje shipyard, who bowed deeply in front of television cameras.
The company said it believed the accident was a result of a miscommunication between crane drivers and signal people, although the exact cause was still under investigation.
Crane drivers at the yard rely on walkie-talkies to receive instructions.
Yonhap news agency quoted a company official as saying it had not had such a big accident for "several years".
It is the latest blow to the corporate empire, the heir to which is currently on trial for bribery in connection with the scandal that brought down president Park Geun-Hye.
A Samsung Heavy Industries spokesman told AFP the Total project, which was due for delivery by mid-June, "may be delayed a little bit".
Police said 12 crane drivers were under investigation as they look into potential operational mistakes or violation of safety regulations.
Eyewitness? Submit your stories now via social or:
Email: news@pulselive.co.ke
