Police had set up roadblocks to prevent vehicles carrying protesters from reaching the city of Manzini, where the rally was due to take place.
“They started by targeting the leadership of the trade union movement, they detained almost all of them,” Zakhele Mabuza, spokesman for the banned opposition People’s United Democratic Movement of Swaziland (Pudemo) told RFI.
Then anyone else known to belong to unions or political organisations was also arrested, Mabuza says, along with anyone wearing red – the protest movement’s chosen colour.
Those detained were taken to regional police headquarters in trucks, he says.
Other people complained of being hit with batons and fired on with teargas and water cannon. Several foreign journalists were also detained.
According to a police spokesperson, the demonstrators were arrested because of reports that they planned to overthrow the government.
The protest, called by a coalition of civil society and trade unions, was prompted by several issues, explains Zakhele Mabuza, the chief demand being political reform.
Swaziland has been ruled for the past 25 years by King Mswati III, an absolute monarch said to have a personal fortune of more than 70.6 million euros.
“This system of governance in Swaziland is outdated, it is undemocratic, it is not giving any tangible positives or development for the people,” Mabuza says. “It is high time that we introduce constitutional, multi-party democracy.”
The protest was banned by the authorities, who arrested several of its organisers over the past week.
It follows a large demonstration last month in Mbabane.