Three maintenance workers were killed at a commercial residential complex building in Seoul on Friday, apparently after being electrocuted while replacing water pumps of the building's water storage tank, firefighters said.

According to the fire authorities, the three men -- two in their 50s and one in his 60s -- collapsed while replacing a water pump in the second underground level of the building in the southwestern ward of Yeongdeungpo late Friday morning.

The workers received CPR from firefighters on the scene before being taken to hospital where they were pronounced dead at 2:11 p.m., firefighters said.

The authorities speculated that two of them may have been electrocuted during the pump replacement work and the third apparently died from electric shock while attempting to rescue the two.

The police said they are currently investigating the exact cause of the accident. (Yonhap)