Clashes broke out in Omdurman, central Sudan, near Wad Nubawi mosque on Friday after demonstrators gathered following activists' call for mass protests.
According to activists, police fired tear gas to disperse protesters causing breathing difficulties.
On Twitter, many also reported assaults on demonstrators.
Rubber bullets were also used against protesters, as well as "machetes and light weapons" in other areas according to Sudanese blogger Muhammad Osman.
Protests erupted in many other places across the country including in Kassala, Bara, Wad Madani, Kordofan, Bahri, and outside the Grand Mosque in al Obeid.
Riot police surrounded mosques in the capital of Khartoum, but also in Omdurman and Bahri in anticipation of today's protests, witnesses said. Pictures posted on Twitter also showed demonstrators wearing face masks ahead of the demonstrations.
Friday's protests have been the most important since last Saturday's security crackdown on protesters.
On June 16, students took to the streets of Khartoum after President Omar Al-Bashir announced a series of austerity measures aimed at reducing the government $2,4bn budget deficit. The movement gained momentum as the days passed transcending mere student activism to include calls for an end to the 23-year-old regime of President Omar Al-Bashir.
On Monday, Sudan's president Omar al-Bashir tried to downplay the movement and described the protesters as "bubbles" before adding that Sudanese demonstrations were different fron the series of protests that swept across the Middle East and North Africa.
Activists have called for more protests on Saturday to mark the 23rd anniversary of the military coup that brought Bashir into power.
Photos via @bluemania26, H.M, @Tahir3T @Shamarat @Usiful_ME