"As of now, about 30 people have been detained and taken to the territorial police departments", Ganusevich said.
Earlier in the day, students from several universities staged unauthorised protests in Minsk.
The Internal Affairs Ministry said that around 1,000 people participated in opposition protests throughout the country on 4 September, while 1,500 people took part in pro-government rallies. Belarusian police have detained 41 protesters for violating a law on mass gatherings.
Belarusian President Alexander Lukashenko stated in August that the unrest in the country is ruining Belarus' economy.
The early days of the demonstrations in Belarus were marked by police violence. Over 6,700 people have been detained, and hundreds have been injured, including more than 130 law enforcement officers. According to the Belarusian Interior Ministry, three people have died during the protests.
Protests have also hit the country's major companies, including vehicle and fertilizer manufacturers - which could deal a potential blow to the country's economy. Speaking with factory workers last month, Lukashenko stated that those who intended to strike could leave if they wanted to, while adding that such protests are ruining the country's economy.