Protesters marched in Mbabane last month to call for democracy in Africa's last absolute monarchy [Reuters]

Police in Swaziland have fired water cannons at pro-democracy protesters and detained people on the streets to prevent demonstrations in sub-Saharan Africa's last absolute monarchy.

Simantele Mmema, a spokeswoman for the Swaziland National Association of Teachers, said on Tuesday that more than 1,000 protesters who were singing and chanting in a teacher's training centre were dispersed by police using water cannons.

Mmema said teachers left the centre and were marching to the centre of Manzini, the economic hub of southern Africa's usually peaceful mountain kingdom.

An online campaign has tried to rally support for the demonstrations, which come exactly 38 years after the current Swazi king's father, King Sobhuza II, banned political parties and abandoned the country's constitution.

A police spokeswoman, Wendy Hleta, said union leaders were being questioned over threats to overthrow the government they allegedly made to foreign media.

COSATU, the biggest trade union federation in neighbouring South Africa, said police arrested seven labour leaders on Tuesday morning.

A South African radio station said one of its reporters had been detained in the country, where she was sent to cover planned pro-democracy protests.

Talk Radio 702's report followed a statement from a pro-democracy group in the country that several activists had been arrested ahead of planned protests.

Mswati's grip on power

The protest has been called by a coalition of civil society and trade unions marching under the banner of the Labour Coordinating Council.

Unions have taken the place of banned parties and are at the forefront of the protest calls - similar to those in north Africa that have toppled presidents in Tunisia and Egypt.

King Mswati III, who has 13 wives and a fortune estimated at $100m in a country where 70 per cent of people live on less than a dollar a day, has refused to loosen the monarchy's grip on power.

Forbes magazine lists the 42-year-old king among the 15 richest monarchs in the world. He assumed the throne in 1986 at the age of 18, has a penchant for fast cars, luxury palaces and extravagant parties.

Police commissioner Isaac Magagula said the police, the army and correctional services were ready to face down "evil" protesters.

"Such evil will not be tolerated," the Times newspaper, a privately owned publication, quoted him as saying.

Police have been raiding activists' homes since last week, with four key protest organisers arrested on Monday.

Last week the national organiser of the banned Swaziland Youth Congress, Mcolisi Ngcamphalala, said he was held and tortured by police for 24 hours.

The prime minister, Barnabas Dlamini, has declared the demonstrations illegal and warned that anyone who took part did so at their own risk.