Although production was only halted for 10 minutes, even a short stop can render some panels obsolete.

"Samsung may have to report some costs, because around 70 percent of panels which were in the process of production during the blackout become useless," said an analyst who declined to be identified.

Shares in Samsung Electronics, tumbled 3 percent in morning trade, underperforming a 0.7 percent decline in the broader market.

Samsung, which competes with local rival LG Display and Japan's Sharp Corp, has since restored 60 percent of production and has said it expects the lines to return to full output later on Friday.

The lost output, mainly large-sized panels for TVs and computer monitors, is unlikely to have major impact on sales or global LCD market, where supplies are plentiful due to weak consumer demand.

The plant in Tangjeong, southwest of Seoul, houses Samsung's most advanced LCD production lines. The four lines have a combined monthly output capacity of 320,000 panels.

Its parent Samsung Electronics separated out its loss-making flat-screen business in April to combine it with a more promising AMOLED (active matrix organic light-emitting diodes) flat-screen operation, currently used mainly in high-end smartphones.

(Reporting by Miyoung Kim; Editing by Edwina Gibbs)

• A Permanent Economic Emergency