Incumbent leader Robert Mugabe, 84, who has ruled Zimbabwe since 1980 and over the past eight years overseen the once prosperous nation's slide into chaos and destitution, is widely expected to cling on to the presidency, using his powers to rig the vote.
Election observers from Europe and the United States have been barred from monitoring the polls. Observers dismissed the country's 2002 election as fraudulent, prompting Western powers to slap sanctions on Zimbabwe, measures that Mugabe blames for his country's desperate plight.
Morgan Tsvangirai of the opposition MDC party and independent Simba Makoni, a former loyalist of the ruling ZANU PF party, are challenging Mugabe for the presidency.
Polls will close at 7:00 p.m. local time (17:00 GMT), and preliminary results are set to be announced by Monday.
If none of the three candidates garner over 50% of votes, an election run-off will be held in three weeks.
Many voters are desperate for change in Zimbabwe, where local cash is next to worthless with the 100,000% inflation rate, and the HIV virus is spreading unabated. Severe food and medicine shortages have caused a steady decline in life expectancy.
The Zimbabwe Conservation Task Force said last year that economic woes have been accompanied environmental disaster, with 60% of the country's wildlife killed off as hunters search for food. Chaos in the country has also brought about mass deforestation and water pollution.
The economy's meltdown began in 2000 with the government's campaign of forced land redistribution. After thousands of white farmers were evicted, mismanagement and corruption set in, crippling agriculture.