At least 12 were killed Saturday when their work bus slipped into Mariotiya river canal in Giza's Haram district, according to the health ministry.
Another 15 were injured in the accident, health ministry spokesperson Hossam Abdel-Ghaffar told Ahram Online.
The bus, which belongs to Orascom construction, was transporting 36 of the company's employees when the accident happened.
Bodies were pulled from the water while civil protection forces are trying to retrieve more bodies believed to have sunk. The death toll is likely to rise.
Local security forces sent a winch to pull the bus from the lake and the road was blocked.
Traffic accidents, which official statistics say claim 18 lives a day, are commonplace in Egypt due to ill-maintained roads and railways as well as disregard for traffic laws.
Earlier in March, seven people were killed — including children — and 26 others injured in a collision between a school bus and a train on a highway connecting Cairo to the northeastern city of Ismailia.