MTR officials on Thursday apologised for the inconvenience caused by the five-hour disruption of the Tseung Kwan O Line and revealed there were signs of a short circuit in overhead cable components.

Speaking at a press briefing, the railway company said the disruption began at 5.15pm when a circuit breaker tripped in the tunnel between Yau Tong and North Point stations.

The incident led to a cascade of failures affecting signal systems across the line, including routes to Po Lam and Lohas Park, the MTR said.

KH Lee, the MTR's chief of operations engineering maintenance, said preliminary investigations showed signs of a short circuit in overhead cable components, with passengers reporting flashes, smoke, and noise.

"As there are a number of trains involved in the particular section of the traction stone, we have to remove the train one by one. And in the course of the train removal, we also found the flashover, and causing the overhead line to trip again," he said.

"After all the trains were removed from the site, we have a detailed inspection on the concerned section, and we also find the flashover mark. We will have a further investigation and inspection on the concerned section."

Cheris Lee, who heads the corporation's operating and metro segment, said the situation was complicated by a traffic accident in the tunnel area.

"The incident happened during the late peak hours and there was very serious traffic congestion outside the Tseung Kwan O area, especially through the tunnel," she said.

"That's why traffic congestion in the area was very serious and also delaying the arrival of the shuttle buses. So we apologise for the inconvenience caused again."

Lee noted that more than 130 staff were deployed for crowd control and passenger assistance.

The Transport and Logistics Bureau said it has asked the MTR to thoroughly review its system and report to the Legislative Council on Monday.