One eyewitness, Henry Langston, told the BBC that the rioters, mainly young people, attacked police with metal poles, dustbins, anything they could get their hands on.
Police used rubber bullets and tear gas after about 100 protesters tried to breach a security cordon. A number of protesters and policemen were reported hurt.
The violence later died down. Mr Langston said the city centre was a mess of rubble, rubbish, and smashed windows.
Earlier the protesters, many brought in by bus from all over the country, had filled a central square in a show of support for a man they still consider a hero.
"I came here to protest against Karadzic's extradition," said Slobodanka Sanojevic, 60.
"He is a great man, he created a state for Serbs (in Bosnia) and saved Serbian children from genocide."
Advertisement
Protesters and police clashed in the streets
BBC regional analyst Steven Eke says the radicals picked up nearly one-third of the vote in May's election and represent many ordinary Serbians who reject further integration with the West.
The US embassy had sent an e-mail to American citizens living in Belgrade urging them to avoid the central area and "exercise caution".
Protests in February on the issue of Kosovo's independence saw part of the US embassy burned. Small scale protests this week have led to clashes in which journalists were attacked.
Radical Party leader Aleksandar Vucic said Tuesday's protest was "against the treacherous and dictatorial regime" of Serbian President Boris Tadic.
Mr Vucic told the crowds that "thieves and bandits are ruling Serbia", adding: "We will fight for Serbia and Serbia will be free."
Mr Tadic said on Tuesday that Europe wanted a Serbia governed by law and promised that "order will be kept".
Extradition wait
Mr Karadzic faces 11 charges, including genocide and crimes against humanity during the war in Bosnia in the 1990s.
EU ambassadors meeting in Brussels on Tuesday stopped short of offering Serbia any immediate prospect of joining the EU following the arrest.
Instead they decided to defer a decision on unfreezing trade benefits until they saw Mr Karadzic transferred to The Hague.
Serbian judges say they have still not received an appeal from Mr Karadzic's lawyers against his arrest.
A lawyer said he had sent the appeal documents by post from a remote location in Serbia before the Friday deadline in an apparent attempt to delay the process.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.
Bookmark with:
What are these?