Two crew members of an Egyptian dredger were killed and two were missing feared drowned when it sank in the Suez canal.
The major international waterway, which averages 7% of world shipping traffic, was closed briefly while ships were diverted to a second channel.
The accident is the latest in a series of transport disasters in Egypt, mostly blamed on negligence and poor upkeep.
More than 1,000 people died when a ferry sank in February, and 58 died when two trains collided in August.
About 50 people on board the dredger Khattab were safely brought back to shore, canal officials said.
The cause of the accident was not immediately clear, but one worker on the dredger said one of its pumps had exploded, causing the ship to sink within minutes.
Canal authorities are currently engaged increasing its depth, so that vessels with a greater draft such as supertankers can go through.
Dredgers are deepening the waterway from 20m (66ft) to 23m (72ft).
At the moment, supertankers must offload part of their cargo onto separate boats and reload at the other end of the canal.