A quarter of Swazis between the ages of 15 and 49 are believed to be HIV positive [AFP]

Hundreds of people have taken to the streets in Swaziland protesting against poor governance which has led to a shortage of essential medical supplies in sub-Saharan Africa's sole absolute monarchy.

More than 500 people demonstrated in Mbabane, the capital, on Wednesday while nearly 1,000 protested in the western town of Siteki.

AIDS groups have warned of an imminent shortage of anti-retroviral drugs in a country where a quarter of the people between the ages of 15 and 49 are believed to carry HIV.

The protests followed failure of labour union negotiations this week.

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Wandile Sifundza, a teachers' union leader, said members want a change to a constitutional monarch in the southern African country, who can be trusted to manage national finances.

Protests were peaceful but heavily guarded. Several students were detained.

Human rights activists criticise the lavish lifestyle of the wealthy king Mswati III.

Mswati, 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.

Last April police fired water cannons at pro-democracy protesters and detained people on the streets to prevent demonstrations.

More than 1,000 protesters chanting in a teacher's training centre were dispersed by police using water cannons.