Zambians are casting their ballots in a presidential election pitting incumbent President Hakainde Hichilema against former minister Brian Mundubile. Polls opened at 6am (04:00 GMT) on Thursday in a race dominated by economic concerns, and are expected to close at 16:00 GMT. Some 8.7 million people are registered to cast their ballots. Results of the presidential vote are expected by August 17. The winner needs more than 50 percent of votes to avoid a run-off.