Last week, the semi-privatised MTR Corp said a subcontractor, Fang Sheung Construction, cut corners when building platforms for the new link under Hung Hom station.

Lam – whose announcement preempted the MTR Corp’s submission of a report into the furore, scheduled for Friday – said the commission would investigate the cause and extent of the problems on the job. It would also review supervision at the MTR Corp and how the government – which has a 75 per cent stake in the corporation – monitors and controls such projects, she said.

She said she had the “full support” of Chief Justice Geoffrey Ma Tao-li to appoint a commission of inquiry, something legislators had pressured the government to do in recent days. She said she would consult her Executive Council on the composition of the panel and its terms of reference, but did not set a date for its formal appointment.

“We hope that the commission can submit its report in about six months’ time after its commencement of work so that the truth can be unveiled as soon as possible,” Lam said.

She added it was “too early to say” whether the probe would delay the opening of the first part of the link, set for mid-2019.

Lam said that, as the commission would be formed under the Commission of Inquiry Ordinance, it would have “all necessary powers” to summon witnesses and request documents.

Under that ordinance, the commission can issue an arrest warrant for anyone who refuses to attend one of its hearings. Anyone who refuses to hand over documents it requests can face three months in jail and a fine of HK$1,000 (US$127).

The law protects witnesses from any criminal or civil proceedings that arise from honest cooperation with the commission.

After the investigation, the commission would make recommendations to safeguard the quality of works and public safety, Lam said.

The city leader said the government would make no “guesses” or premature announcements on whether MTR Corp chairman Frederick Ma Si-hang would lose his job.

“Chairman Ma has worked hard in leading the MTR Corp in the past three years,” she said.

Bad news and scandal are piling pressure on Hong Kong's MTR

In a report delivered in January 2015, the panel found that the Highways Department and the MTR Corp had respectively failed in their roles, resulting in delays and a budget overrun. The MTR Corp’s corporate culture of “discouraging elevation of bad news without solutions” was partly to blame, the panel said.

China Technology Corp, one of two subcontractors, along with Fang Sheung, working under Leighton on the Hung Hom platforms, said it welcomed the government’s announcement and would “actively cooperate” with the investigation.

Leighton Contractors (Asia) refused to comment on the matter.

The MTR Corp said its board welcomed the probe and had instructed its management to “fully cooperate” with it.

“If any violation is found as a result of the investigation by the commission, it would be treated very seriously and handled strictly in accordance with the law,” a spokesman said.

Democratic Party lawmaker James To Kun-sun said, that given the legal protections on offer, he expected anyone summoned to cooperate and tell the commission what it wanted to know.

“If you don’t say it, the other party might,” he said.