Zeinobia at Egyptian Chronicles describes what has happened:
This is how it began on January 25th when the police forces attack the protesters at Tahrir square at night after midnight and this is why I am so scared now !!
The military police has attacked the protesters who were having a sit at Tahrir square and at the cabinet HQ at Kasr Al Aini street. Protesters have been chased and eye witnesses are saying that teasers and whips were used, activists have been detained. No one is allowed to enter there, journalists were not allowed to cover what is going on. There are reports that masked men with machine guns were seen with the military police, I think they were brought to scare the protesters.
The New York Times provides more details:
The first sign of tension arose when hundreds of people rallied in the intersection in front of the prime minister’s office, barred from taking their protest any closer to the ornate building by armored personnel carriers and a line of soldiers armed with Tasers.
The crowd returned to a chant heard often in the days before Mr. Mubarak fell, replacing his name with the prime minister’s: “The people want the overthrow of Ahmed Shafiq!”
Military police surrounded the protesters and kept them from leaving until late at night, witnesses said, while in Tahrir about a thousand people began to pitch tents and settle in for the night.After midnight, soldiers and police officers took over the square.
Salma Said was asleep in a tent when it began to fall down on top of her. Outside people were screaming, and she emerged to see people being beaten by soldiers and armed plainclothes security officers wearing masks.
“They had their faces covered like criminals,” she said, “They only showed their eyes.”
“One of the officers threatened to shoot us and said he was going to set our tent on fire,” she said.
Now Al Jazeera tells us:
“6 am: Military police place barbed wire on all roads leading to Tahrir”
Egyptian protest facebook pages are calling for a return to the Square Saturday morning:
Peaceful protesters in Tahrir are being chased away by military police with Tasers, sticks & whips in Tahrir square. Masked men with machine guns trying to shut down the strike by force. Many beaten, assaulted and arrested.
We cannot stand for this, we must stand strong against violence towards peaceful protesters.
Al Masry Al Youm quotes one of those in the Square:
“I am one of thousands of people who stood their ground after the army started dispersing the protesters, shooting live bullets into the air to scare them,” said protester Ashraf Omar.
“They were using tasers and sticks to beat us without any control. I thought things would change. I wanted to give the government a chance but there is no hope with this regime,” Omar said. “There is no use.”
“I am back on the street. I either live with dignity or I die here.”