Voter queues have been long despite the heat
A court in Namibia has ruled that the National Society for Human Rights must have its status as an election observer reinstated, hours after polls opened.
The electoral commission withdrew the group's status days before the vote, saying it was not impartial.
A BBC reporter in the capital says there are long queues despite the heat.
Swapo ruling party candidate President Hifikepunye Pohamba faces his strongest challenge from former Foreign Minister Hidipo Hamutenya, analysts say.
His Rally for Democracy and Progress (RDP) broke away from Swapo in 2007.
There are 10 other presidential challengers.
President Pohamba, seeking his second five-year term, was among the first to vote in the capital Windhoek.
NAMIBIA GENERAL ELECTIONS
Presidential and parliamentary ballots
12 presidential candidates
72 seats in parliament
1.1m registered voters
Voting on Friday and Saturday
The BBC's Frauke Jensen in the capital Windhoek says many people are in the queues with umbrellas to protect themselves the sun.
She says the NSHR has been extremely vocal in its criticism of the electoral commission.
It says the voters' roll includes constituencies that have been listed twice, voters who have been listed twice and under-age people - a discrepancy of about 180,000 voters. The Electoral Commission of Namibia has rejected the allegations.
But the court on Friday ordered the commission to all polling stations that NSHR personnel are allowed to observe the presidential and parliamentary ballots.
Swapo has dominated Namibia's politics since it gained independence in 1990 after a long struggle against rule by South Africa.