Reports suggest six protesters have been killed in clashes in and around Taiz.
Days earlier, key sites in Yemen’s third-largest city fell to Shia Houthi rebels.
Yemen has now asked the United Nations to back military action to battle the Shi’ite militia advance.
There are fears Yemen is heading for civil war. In a letter to the UN, Yemen’s official president, Abed Rabbo Mansour Hadi has reportedly asked for the help of ‘willing countries’ to ‘deter the Houthi agression.’
Thousands have taken to the streets to demonstrate in the southwestern province – also called Taiz – in an attempt to defend their towns.
Militants fired bullets and teargas to disperse the demonstrators.
The Houthi rebels seized the capital Sana’a in September and are said to be closing in on Aden, where the President Hadi is based.