The MTR Corporation knew about a defective batch of electrical insulators before one caused three hours of disruption on the East Rail Line on Tuesday, operations director Dr Jacob Kam Chak-pui said.
Kam also said the company would seek to hold the unnamed European supplier responsible.
Transport minister Professor Anthony Cheung Bing-leung says the government will monitor the MTR's performance and ask it to review maintenance work.
Watch: Hong Kong's MTR during peak hours
The most serious disruption on Tuesday was between Tai Po Market and Lok Ma Chau, where trains in both directions had to use the same track.
It was the second incident caused by the same batch of insulators in 10 days. Kam said in an RTHK interview that after the first incident on February 9, the company had conducted a detailed investigation and discovered the quality of the batch was not up to standard.
It had started replacing the insulators, and finished the replacement of four, before the second incident occurred. He did not explain why the company did not inform the public about the test results after the investigation.
The MTR Corp is replacing the other 65 insulators from the same batch and expects the process to be completed in 10 days. Kam said eight or nine of them were replaced on Tuesday night.
Without naming the "famous European brand" Kam said: "We will definitely pursue responsibility from the provider."
Cheung said the government would keep an eye on the MTR's performance and would follow up on its contingency measures, after information in MTR leaflets was found to contain scrapped bus routes on Tuesday.
Other platforms, such as those in Admiralty station and Kowloon Tong, also became more crowded following the disruption. The MTR had to close gates at Admiralty.
"We will request the MTR to review its maintenance work and potential problems in a comprehensive manner," Cheung said.
An East Rail insider said the line was built under a British system and many components were from the UK. The last time a similar incident occurred on the East Rail was 15 years ago. After that, former operator Kowloon-Canton Railway began inspecting parts bought from outside Hong Kong more carefully, especially those from the mainland, the source said.
Lawmaker Michael Tien Puk-sun, a former KCR chairman, said the MTR was slow in reacting to the first incident.
"They should have held the supplier accountable right after the first incident, and asked them to send a new batch to it immediately," Tien said.
He said the railway should also rethink whether overhead cables were the safest options to provide electricity to trains.