Namibians returned to vote on Friday in 36 polling stations reopened two days after a chaotic election, set to test the ruling party's 34-year grip on power, was marred by technical problems.

Tensions are mounting in the historically stable and peaceful southern African nation where Wednesday's election was marked by long delays and labelled a "sham" by the opposition.

Some people waited 12 hours in line to vote in presidential and legislative polls, billed as the toughest yet for the South West Africa People's Organisation (SWAPO) party, in power since Namibia's 1990 independence from South africa.

Wednesday's queues were caused by many technical problems, including issues with tablets used to register voters and shortages of ballot papers.

In some cases, torches used to show up invisible ink had run out of batteries and mobile voting teams had left areas with voters still in the queues, it said.

Facing criticism from both voters and parties, the electoral commission extended the vote for a second time, giving Namibians until Saturday evening to vote.

In the capital Windhoek, at the only polling station picked to reopen, about 60 people showed up on Friday, including Kluivert Muuondjo who arrived at 4:30 am.

The 21-year-old student said he had waited in line until 11:00 pm on Wednesday but left before being able to vote as he had exams the next day.

"Everyone will have the chance to vote," he said. But because Namibians can vote at any given polling station, he was worried "everyone will flock to one place again."

The disarray led to angry complaints from opposition parties with some calling for a halt in the electoral process.

Opposition parties were scheduled to meet on Friday and issue a joint statement, according to Christine Aochamus who represents the Independent Patriots for Change (IPC) party.

Youth unemployment, enduring inequalities and the emergence of a generation born after independence are challenging support towards SWAPO which has ruled since 1990.

Its candidate, vice-president Netumbo Nandi-Ndaitwah, who could become the first woman to lead the country if elected, could face an unprecedented second round in the mineral rich country.

"To open only one place in Khomas (the region of which the capital is part of) is absurd," said voter Ensley Engermund, who also said he couldn't vote on Wednesday because of long queues despite trying four different polling stations.

"Only 1.5 millions voters are registered and we get this chaos?" asked the 49-year-old security agent.

"It was to get people frustrated."