Egypt's ruling Supreme Council of the Armed Forces has announced three days of national mourning after at least 74 people died in clashes between rival football fans in the city of Port Said.
Hundreds more were injured as fans invaded the pitch after a match between top-tier clubs al-Masry and al-Ahly.
Emergency meetings of the cabinet and parliament have been called.
Protest marches are being planned for Thursday against the police's inability to contain the violence.
One al-Ahly fan told the BBC that fans will march from the al-Ahly's club in Cairo to the Interior Ministry.
"People are angry at the regime more than anything else... People are really angry, you could see the rage in their eyes," Mohammed Abdel Hamid said.
Football fans in Egypt can be violent, and certainly there is a bitter rivalry between these two teams.
The al-Ahly fans, known as Ultras, have a particular reputation for violence.
But lately they have been at the forefront of clashes with the police.
On the social media, there has been speculation - and I hasten to add there is no evidence - that the security forces may have had an interest in taking on al-Ahly supporters.
Certainly riot police did not seem to be very effective, they were standing around, but maybe there simply were not enough there.
Hundreds gathered at Cairo's main railway station to receive the injured and the first bodies arriving from Port Said, with some chanting slogans against military rule.
Field Marshal Hussein Tantawi, the head of Egypt's ruling army council, went to an airbase near Cairo to meet al-Ahly players who were flown back from Port Said on a military aircraft.
"This will not bring Egypt down... These incidents happen anywhere in the world. We will not let those behind it go," he said, according to Associated Press.
It is the biggest disaster in the country's football history, said the Egyptian deputy health minister.
"This is unfortunate and deeply saddening," Hesham Sheiha told state television.
Some of the dead were security officers, the Associated Press news agency quoted a morgue official as saying.Tense atmosphere
The BBC's Jon Leyne in Cairo says it appears some fans had taken knives into the stadium.
Our correspondent says the lack of the usual level of security in the stadium might have contributed to the clashes.
Police in Egypt have been keeping a much lower profile since last year's popular protests that ousted President Hosni Mubarak from power.
Egyptian fans are notoriously violent, says our correspondent, particularly supporters of al-Ahly known as the Ultras.
They have been heavily implicated in confronting the police during recent political protests, our correspondent adds. There is speculation that the security forces may have had an interest in taking on al-Ahly supporters.
Wednesday's violence broke out at the end of the match, which, unusually, Port Said club al-Masry won 3-1.
Witnesses said the atmosphere had been tense throughout the match - since an al-Ahly fan raised a banner insulting supporters of the home team.
As the match ended, their fans flooded onto the pitch attacking al-Ahly players and fans.
A small group of riot police tried to protect the players, but were overwhelmed.
Part of the stadium was set on fire.
Officials say most of the deaths were caused by concussions, deep cuts to the heads and suffocation from the stampede.
"This is not football. This is a war and people are dying in front of us," al-Ahly player Mohamed Abo Treika said.
"I cannot believe these things happened randomly, I don't think so, it was arranged," Al-Ahly official Hanan Zeini told the BBC.
Meanwhile, the Muslim Brotherhood - which has emerged as Egypt's biggest party in recent elections - blamed supporters of ousted President Hosni Mubarak for the violence.
"The events in Port Said are planned and are a message from the remnants of the former regime," Muslim Brotherhood lawmaker Essam al-Erian said.
He went on by saying that the army and police wanted to silence critics demanding an end to the state of emergency in the country.