The safety of repair workers should be prioritised over a speedy resumption of public transport services, lawmaker Gary Zhang said on Friday, as parts of the Kwun Tong line remained shut after being hit by heavy downpours.

Wong Tai Sin MTR station was severely flooded when the Black Rainstorm Warning was in effect.

Photos circulating online showed repair workers working in at least chest-deep in water, with the Hong Kong Federation of Railway Trade Unions saying the MTR Corporation had confirmed the images as genuine.

The railway company stressed that power had been cut off before the relevant repair works began, adding that it had been in touch with frontline maintenance staff to ensure their safety.

But Zhang, who was previously an engineer with the rail giant, wrote on social media that he was approached by frontline staff who were in near emotional breakdown about being sent to the flooded tunnels.

He said he wouldn't have allowed any of his colleagues to risk their lives if he was in charge, and that he had requested intervention from the MTR's management.

Zhang stressed repair staff should be given comprehensive personal protection equipment when carrying out such works.

"Although resuming services is very important to the local community and to our city, their safety is the first principle when doing repairs. We should never put our workers, our maintenance colleagues at risk," he told RTHK.

The Hong Kong Railway Workers General Union also said the MTR's arrangement had not been ideal, and should've put the safety of its staff first and provided them with more protective gear.

Roundtable lawmaker Michael Tien, for his part, called for more information from the railway company on why workers were sent to Wong Tai Sin station.