Street vendors have clashed with riot police in Mexico's colonial city of Oaxaca after they were prevented from entering Oaxaca's main Zocalo square by the local government.

Some 100 demonstrators converged close to the main square, where federal police wearing body armor stood shoulder to shoulder.

At one entrance to the square, protesters lobbed rocks and bottles at police, who responded with volleys of tear gas.

The scuffles broke out as street sellers, from the indigenous town of Santos Reyes Nopala, tried to reach the square in order set up their stalls selling goods such as crafts and regional clothes. The vendors had occupied the square in the city, famed for its colonial architecture, exotic food and indigenous culture, since June this year.

Local media reported three protesters were arrested. No serious injuries were reported.

The square was barricaded by police in order to prepare for the annual "Radish Night," a unique festival held during the Christmas season, where radishes are sculpted into complex figures that compete for prizes.

In 2006, Oaxaca City, a popular tourist resort, was rocked by a six-month conflict in which leftist activists tried to bring down Oaxaca's governor, who they accused of stealing an election, corruption and heavy-handedness.