Survivors say a fire blazed for hours on a Red Sea ferry before it sank, leaving 1,000 people feared dead.
The fire broke out soon after the ship left Saudi Arabia, but it sailed on towards Egypt for two hours before finally sinking, angry survivors say.
Around 350 people have been rescued, but most of the other estimated 1,400 people on board are feared lost.
Unrest broke out in the Egyptian port of Safaga as relatives desperate for news clashed with riot police.
The relatives have grown increasingly frustrated at what they say is the lack of information from the authorities.
Some threw rocks and stones at police as the clashes broke out. Police used sticks and tear gas to try to restore order.
"They are not telling us anything," shouted a man named Gedir Mohammed, according to the Reuters news agency.
"Where are the corpses? Where are they taking the survivors?" he asked.
Survivors say the blaze on board the al-Salam Boccaccio '98 started soon after it set sail from Duba in Saudi Arabia on Thursday night.
Some claim the Saudi port was still in view, but the ship sailed on.
One survivor coming ashore at the port of Hurghada shouted: "It was like the Titanic on fire," according to the AP news agency.
Another man, Rifat Said, told reporters: "There was thick smoke. We asked why and they told us they were putting out the fire but it got worse.
"The ferry sailed on for two hours listing to the side. Then it just went onto its side and within five minutes it had sunk."
Raafat al-Sayyed told AFP news agency that passengers were told to gather on the decks so that crew members could extinguish the blaze.
Another Egyptian, Kamel Mohammad Abdel Askari, added: "But the fire continued for a long time, and they (the crew) kept on saying that they were getting it under control."
An Egyptian minister described the fire as "small" and said there was no explosion on board, contrary to reports from some survivors.
Egyptian President Hosni Mubarak has ordered an inquiry into the circumstances in which the 35-year-old Italian-built boat sank.
His spokesman, Suleiman Awad, said "the speed at which the ship sank and the fact there were not enough life rafts on board confirm that there was a [safety] problem".
"But we cannot anticipate the results of the investigation," he told public television.
Most of the passengers were Egyptians working in Saudi Arabia, but some were said to be pilgrims returning from Mecca.
No distress signal was said to have been received by Egyptian officials before the ship went down.
Warships and helicopters have been searching the area, which Ayman al-Kaffas, spokesman for the Egyptian embassy in London, described as "vast".
RECENT SHIPPING DISASTERS
2002: Joola, Senegal, more than 1,800
2001: Java, Indonesia, more than 500
1996: Bukoba, Tanzania, more than 500
1994: Estonia, Baltic Sea, 852
1991: Salam Express, Egypt, 464
1987: Dona Paz, Philippines, more than 4,300
Twenty-two more survivors were picked up by Saudi rescue vessels, reports on Saturday said, but officials fear there is little hope of finding others alive more than 36 hours after the tragedy.
Weather conditions have hampered the rescue operation, with high winds and choppy seas.
A British warship sent to the area has been recalled after Egypt said it was no longer needed.