MEXICO CITY (AFP) - Anti-riot police stormed Mexico City's historic centre to remove striking teachers on Friday, using water cannon to clear the area while protesters responded with firebombs.
Hundreds of federal officers broke through barricades, chasing out a few hundred protesters who had disobeyed a deadline to vacate the Zocalo Plaza ahead of the nation's independence day celebrations this weekend.
At least 29 demonstrators were injured in the clashes, the Red Cross said.
The National Security Commission said at least 11 police officers were injured while 29 "anarchists" were detained.
Thousands of teachers had been living in a tent city in the square for the past three weeks to protest a major education reform championed by President Enrique Pena Nieto, but most had cleared out before the ultimatum.
After the police took back control of the Zocalo - home to the National Palace, Aztec ruins and the city's cathedral - clean-up crews came in to pick up trash and plastic tarps ahead of the celebrations on Sunday and Monday.
Some 200 protesters had placed metal barriers and set small trash fires in adjoining streets, throwing rocks and Molotov cocktails at the charging police.
Clashes continued along the city's avenues with hundreds more protestors, with some swinging clubs at the officers, who fired tear gas.
Minutes before the police moved in, Mr Nieto's government released an invitation to the holiday celebrations, with his appearance at the National Palace late on Sunday to deliver the annual "Cry of Independence" and a military parade on Monday.
Teachers who had agreed to leave the Zocalo moved their camp to the city's Revolution Monument.
The dissident National Education Workers Coordinator (CNTE) union led several protests in the city for the past three weeks that failed to stop the passage of an overhaul of the education system, which ranks last in the 34-nation Organisation of Economic Cooperation and Development.
Their demonstrations disrupted traffic in the already congested megalopolis, and twice they blocked road access to the international airport.
The demonstrations irritated many "chilangos", as Mexico City residents are known, with 59 per cent favoring the use of force against the teachers, according to a poll conducted last month by Reforma newspaper.
National police chief Manuel Mondragon y Kalb had warned earlier that the officers would clear the Zocalo after the deadline passed "otherwise this will go on forever and we will never resolve the issue". Mr Nieto signed the reform this week in order to break the hold unions have on education, and to require teachers to undergo mandatory performance evaluations.
The teachers say the new rules violate their labour rights and fail to take into account conditions in rural and indigenous regions.
The new law is among the major structural reforms that Mr Nieto has pushed since taking office in December.
His plans to open the state-controlled oil sector has also sparked protests, but his centrist Institutional Revolutionary Party has struck a pact with conservative and leftist rivals to enact reforms that all agree are needed.