Thousands of people rallied Saturday in a demonstration by the opposition Unita, to celebrate a surprise court victory that forced the national elections chief to step down months ahead of polls.

Dressed in T-shirts emblazoned with a photo of Unita boss Isaias Samakuva, with many wearing caps in the party's trademark red and green, thousands sang and danced in a plaza in the Angolan capital.

"Free, fair and transparent elections, respecting the law," was the slogan of the rally held months before the polls expected from September.

"We are here to demand that the president of the republic ensure that the electoral process unfolds smoothly," Samakuva told the cheering crowds.

"In order for it to go well, everyone must prepare to vote but also to protect their votes," he said.

Unita put the crowds at 10,000, but there was no official estimate from police. Samakuva said more rallies could take place as the election nears.

The party organised similar rallies in Angola's main cities, originally to press its demand for elections chief Suzana Ingles to step down, arguing that she didn't meet the legal requirements to hold the job.

On Thursday, the Supreme Court agreed and ordered her to vacate her post leading the National Electoral Commission.

The ruling caught many by surprise in a nation where the ruling MPLA -- in power since independence from Portugal in 1975 -- has seen few challenges to its power.

Unita, a former rebellion that battled the government for decedes in a devastating civil war -- decided to carry on with the rallies to celebrate its court victory.

This year's election will be only the third in Angola's history.

The first election was in 1992, although it was never completed because the civil war re-ignited, and the second was in 2008, six years after the end of the conflict.

The MPLA won the last vote by over 81 percent and has used its commanding parliamentary majority to pass a raft of new laws including a new constitution, which has abolished direct presidential elections.

The head of state will be chosen from the top of the winning party list in this year's polls, expected to easily hand President Jose Eduardo dos Santos another term in power.