Ethiopian security forces beat rock-throwing students protesting against the result of the 15 May parliamentary election they say was rigged, opposition parties and students said.
A second day of demonstrations turned violent after protests on Monday at Addis Ababa University left one person dead and saw more than 500 arrested.
On Tuesday, about 100 students at a technical college tried to stage a protest march but were forced to stay inside their campus by riot police and paramilitary soldiers, witness Sao Okutsu, a teacher, said.
The ruling Ethiopian People's Revolutionary Democratic Front (EPRDF) and the police have accused the main opposition Coalition for Unity and Democracy (CUD) of inciting the students.
Tension has been rising in Africa's top coffee grower since the election, with the opposition accusing the EPRDF of Prime Minister Meles Zenawi of intimidation and vote-rigging.
"I am weak. I can't tell you what they did to us. They beat us too much on our heads, they pulled our hair, beat our eyes and our feet," said student Aserat Made.
The government imposed a month-long ban on public demonstrations after the polls.
The CUD and the United Ethiopian Democratic Forces said the students had protested because the ruling party was trying to "defraud the public of their votes". They urged the government to release those arrested.
"The harsh measures taken by the government would worsen the already unstable and tense environment and is a great concern," the opposition said in a statement.
On Tuesday, students began throwing rocks, which littered the streets outside the college near the city's Mexico Square, prompting security forces to storm the campus and force the students to the ground, Okutsu said.
"Students sitting on the ground in the campus were being beaten harshly by the police," he said before police hurried him away.
"Students sitting on the ground in the campus were being beaten harshly by the police"
Police fired tear gas to disperse scores of relatives and friends of the students who had arrived to plead for their release.
A student leader said the students would continue to boycott classes until arrested colleagues had been released.
"We can't continue to study unless they release our fellow brothers," said a sobbing 16-year-old student who gave her name as Leya.
Police have been deployed throughout the city, with armed security forces blocking roads with armoured cars to keep pedestrians and journalists away from the college.