The violence happened after police ordered that the route and length of a planned march by students be curtailed.
Some protesters refused, sparking the clashes, in which some witnesses said the police used clubs.
Another report said a protester shot in Sunday’s demonstrations – which also turned violent – had died.
Opponents of President Jean-Bertrand Aristide have clashed repeatedly with supporters and police over recent months. More than 40 people have died in the violence since September.
Monday’s trouble began when police told march organisers not to use a route that would take them close to the president’s supporters and to keep the march to under three hours, reported the news agency Efe.
Police commissioner Daniel Compere said organisers had not given the legally required 48 hours’ notification of the march.
The organisers rejected the demands, accusing the police of allowing supporters of Mr Aristide to gather “when they want and where they want”.
Students and teachers then reportedly gathered outside the state university, throwing stones at police.
Protesters also threw stones at private schools which had refused to shut in solidarity, said the Associated Press news agency.
Police used tear gas to disperse protesters, causing residents in the area to flee too. A tear gas canister also landed in the playground of a girls’ school, leaving pupils gasping, said AP.
Police also reportedly fired live rounds into the air.
Two or three protesters were detained by police, said radio reports. A university professor later alleged on the radio that they had been tortured.
The Haitian legislature has been left in limbo since the mandates of most lawmakers expired last week.
The opposition has refused to accept Mr Aristide’s offer for general elections within six months without his resignation.
Representatives of Caribbean Community (Caricom) are meeting representatives from
Caricom leaders are also expected to meet Mr Aristide, but at a different time and place, said the report.