Makerere University students confront a policeman during protests in Kampala on Tuesday against the age limit bill that will allow the current president, Yoweri Kaguta Museveni, to stand as a presidential candidate again. Picture: Isaac Kasamani /AFP

Kampala - Lawmakers brawled in Uganda's parliament on Tuesday over long-serving ruler Yoweri Museveni's attempt to stay in power by removing presidential age-limits.

MPs shouted, shoved, threw punches and lobbed documents in a fight between ruling party politicians and those from the opposition. At least one MP brandished a chair and attempted to hit his opponent over the head.

Tensions were high over a plan backed by members of President Museveni's party to table a constitutional amendment scrapping age limits, which would clear the way for the 73-year-old to run for a sixth consecutive term in 2021.

Speaker Rebecca Kadaga struggled to control the brawl which broke out after one of the MPs from the opposition Forum for Democratic Change (FDC) -- many of whom were wearing red headbands to protest the proposed amendment -- accused a government legislator of threatening him and of sneaking a gun into the chamber.

The behaviour was no more decorous outside parliament, where police fought running battles with students angry at the proposed amendment.

Hundreds of students at the country's main Makerere University once again defied a blanket ban on protests and marched around campus wearing the red ribbons that have become a symbol of defiance.

Some demonstrators lit barricades and erected makeshift roadblocks as they faced volleys of tear gas from armed officers backed by military police.

Student leader Colins Tumukunde said the constitution was "the soul and character" of Uganda, and they must fight to protect it.

"Our constitution is not written in pencil, it cannot be amended just like that," he said.