At least 10 people have been injured amid efforts by police to stop clashes between demonstrators and government supporters in the centre of the Jordanian capital, Amman.
Police used batons on Friday to disperse people outside city hall, beating and injuring nine journalists.
The clashes took place after about 2,000 people, including Islamists and youth groups, marched from the city's Al-Husseini mosque to the city hall.
An Al Jazeera correspondent and several other journalists, including a Reuters cameraman, said they were attacked by police.
The wounded included an AFP photographer and a female activist.
Al Jazeera's Nisreen El Shamayleh, reporting from the scene of the clashes, said: "The protesters were attacked by riot police and public security personel at the beginning of the sit-in that they were planning to hold at Al Nakheel Square.
"They weren't allowing the protesters to enter [the square] and that is when the clashes started.
"Only after the clashes began and several people were injured that they allowed people to [begin the sit-in]."
Fahim Karim, a New York Times reporter, was beaten by 10 policemen while a photographer who works for another international news agency said he was ordered by police not to shoot the scene.
One protester told Al Jazeera: "During the march the security forces attacked us. We had to make for the women to escape the assault as one woman had already passed out.
Another said he was kicked in the stomach by one of the royal guards while trying to protect "the women in the march".
Besides Amman, rallies for reform and against "rampant corruption" also took place in Tafileh, Man and Karak in the country's south, and in Irbid and Jerash in the north.
Our correspondent said there is a definite feeling in Jordan that there is no serious motivation to implement real and true democratic reforms in the country.
Jordan has faced a protest movement demanding political and economic reforms and an end to corruption, since January.
Security forces have previously prevented demonstrators demanding the removal of the government, but not King Abdullah, who appoints the cabinet and has wide powers, from assembling at main squares.
The clampdown appears to have been prompted by fears of mass crowds as seen in Egypt and Tunisia where long-serving leaders were overthrown earlier this year.