The incident took place near Balmiki Chowk when followers of the religious sect clashed with some Sikhs who were on their way back from a meeting in Gurdwara Dashmi Patshahi, police said.
The meeting was held to chalk out a strategy for seeking action against some Dera followers who had recently attacked few Sikhs near Rania in the district, they said.
All the injured persons were admitted to the General Hospital, where their condition was stated as stable, they said.
According to sources, two jeeps were among the vehicles set on fire by the mob.
The clash was in retaliation of the incident in which some Sikhs had allegedly showed black flags in Ellenabad to Dera Sacha Sauda chief Gurmeet Ram Rahim Singh while he was on way to Rajasthan a few days back, sources said.
Heavy police force has been deployed in the town to prevent any untoward incident. Sources said police personnel from the nearby districts are also being rushed to Sirsa.
Besides enforcing curfew, the district authorities have requisitioned para military forces to help maintain the law and order.
Additional force has been deployed in sensitive locations of the town including areas around Gurdwara Dashmi Patshai, Balmiki Chowk, Shiv Chowk and Begu Road.
Dera Sacha Sauda is a religious sect based in Sirsa, where the situation was tense but under control, sources said.
Shiromani Gurudwara Prabandhak Committee member Sant Gurmeet Singh Tirloke Wala, who was also injured, has appealed to the people to maintain peace and not to believe in rumours.
Deputy Commissioner J Ganesan, has appealed to residents of Sirsa not to step out of their homes and assured them that law and order and peace would be maintained at all costs.
Police force has been deployed all over the city, especially at the General Hospital, Rania road, and around the gurdwara, he said.
"Significant measures have been taken to keep an eye on every part of the city. All Sub-Divisional Officers (civil), Tehsildars, Block Development and Panchayat Officers have been directed to stay in their offices and remain in touch with the police stations," he said.
Meanwhile, INLD Secretary General and Dabwali MLA Ajay Singh Chautala said today's clash was another example of "deterioration" of the law and order situation in Haryana.
He said the tension between Dera followers and the Sikhs had been brewing for the past several days, but the government failed to act on time.
