Hundreds of Sudanese called for "revolution" on Monday, the second day of protests in support of four dead students originally from the conflict-plagued Darfur region.
Their deaths, following a crackdown on a tuition protest at Gezira University south of Khartoum, have sparked the largest outpouring of Arab Spring-style discontent since anti-regime protests in June and July.
A crowd of about 700 people came out of Nilien University shouting "Revolution until victory" and "Killing students is the killing of the nation!", an AFP reporter witnessed.
Police responded with tear gas and some protesters were beaten with batons, he said.
Some scattered into the city's main bus terminal nearby, where several truckloads of riot police were already on standby.
An AFP reporter also observed pickup trucks with plainclothes security agents in the area, the scene of violent clashes on Sunday.
The main road through the bus terminal was charred from a fire which burned during Sunday's unrest when, an AFP reporter said, six people were injured, a bus was torched, and police fired tear gas.
Official radio said 47 people were detained on Sunday when hundreds also protested.
In June and July demonstrations began at the University of Khartoum over high inflation and then spread to involve scattered protests throughout the country, calling for the fall of the 23-year regime of President Omar al-Bashir.
They petered out following a security clampdown.
In 1964, the death of student activist Ahmed al-Qureshi sparked the "October Revolution" which ended the military regime then in power after tens of thousands protested.© ANP/AFP