Pro-democracy campaigners want to embarrass the government
Police have clashed with protesters in the Swazi capital as 20 heads of state began gathering to attend an international conference on sustainable development.
The BBC's Thulani Mthethwa says that office and shop windows were smashed after heavily armed paramilitary police and soldiers fired teargas canisters and rubber bullets to disperse about 2,000 demonstrators in central Mbabane.
About 20 heads of state are to meet to discuss public and private partnership investment in development projects.
The pro-democracy campaigners appear to have timed their action to cause maximum embarrassment to the Swazi government.
'Lack of democracy'
A four-day strike, which started on Tuesday was called by the Swaziland Federation of Trade Unions and the Congress of South African Trade Unions (Cosatu).
King Mswati's government is blamed for 'disregarding the rule of the law'
They say that the Swazi government has violated human rights, refused to recognise judicial orders and intimidated the judiciary.
The secretary-general of the Swaziland federation, Jan Sithole, told BBC Network Africa programme on Wednesday that the union wanted to highlight the "lack of democracy in the country and to protest against a 30% pay rise which politicians had awarded themselves".
"As a result, people are being displaced and evicted from their place of birth - but all and above this the country is not doing well economically, and it has over 30% of its people starving," Mr Sithole said.
The workers had hoped to deliver a petition at the Smart Partnership International Dialogue village where the four-day annual Commonwealth summit is being held.
However, our correspondent says that Swaziland deputy police commissioner, Isaac Magagula said that workers would not be allowed to deliver the petition.
About 500 Cosatu members are protesting on the South African side of the border stopping truck drivers from delivering fuel to Swaziland.
The conference is to be attended by several African leaders, including President Robert Mugabe of Zimbabwe and President Joachim Chisano of Mozambique, the current chair of the African Union.
The South African deputy president, Jacob Zuma, will also be there.
But he is expected to fly in to the country, thus avoiding the blockades on the border.