Singapore's metro authorities have acknowledged that lapses in safety protocol caused the accident on the trackway near Pasir station that killed two maintenance workers on Tuesday.

The authorities said a failure following the simple procedure of coordinating with the signal unit to stop oncoming trains before workers enter the track might have caused the accident.

The Singapore Mass Rapid Transit (SMRT) said its records did not show that such as procedure took place, Channel News Asia reported.

The incident occurred at about 11 in the morning of Tuesday. Both the workers were pronounced dead at the scene by paramedics.

Earlier, senior officials had said the incident happened before the relevant teams had turned off power on the tracks.

"Exactly how they got on to the track, or got close enough to the oncoming train, that was moving in the direction opposite to them, is the issue that we're trying to establish with the witnesses that we are trying to get detailed accounts from," SMRT CEO Desmond Kuek said on Tuesday, CNA reported.

However, officials have not conclude how exactly the victims came under the train. A spokesman had told CNA on Wednesday it was not clear whether the victims were on the trackway or on the walkway when they were hit.

The maintenance staff who died were named Nasrulhudin and Muhammad Asyraf. "We take responsibility and apologise for the tragic accident," SMRT said, adding that it was offering all support to the police and the ministry of manpower in investigations.