Turnout in Liberia's presidential run-off appears low following an opposition boycott over fraud claims and deadly clashes on Monday.
Opposition candidate Winston Tubman said he was pulling out of the vote, but the election commission urged Liberians to cast their ballots.
Nobel Peace laureate Ellen Johnson Sirleaf, Africa's first elected female president, is now the only candidate.
A BBC reporter says her re-election will be tainted unless turnout is high.
The BBC's Jonathan Paye-Layleh in central Monrovia says at the polling station where he was when voting began, just eight people were waiting to cast their ballots, compared to hundreds last month.
Our reporter says he has received similar reports from other parts of Liberia, including the second city, Buchanan.
It seems many people felt it was pointless to vote because Mrs Sirleaf was assured of victory, our correspondent says.go here
She was elected in 2005, in the first election since the end of a 14-year civil war.
Mrs Sirleaf cast her ballot in her home town, Fefee, near Monrovia, promising an investigation into the violence that broke out on Monday, the Reuters news agency reports.
"Liberia is going to move forward. We will find a way to heal the wounds," she is quoted as saying.
Our reporter says UN peacekeepers and Liberian police are searching vehicles entering the city and have deployed tanks at strategic places - including the presidential residence - following Monday's violence.
A UN helicopter also circled the city, he says.
Officials from Mr Tubman's Congress for Democratic Change (CDC) said at least four people died after police opened fire on supporters, but this could not be confirmed.
Ellen Johnson Sirleaf:
* Africa's first female elected head of state
* Harvard-trained economist
* Finance minister before Samuel Doe's 1980 coup
* Twice forced into exile
* Initially backed then-rebel leader Charles Taylor before falling out with him
* Won 2011 Nobel Peace Prize for helping end Liberian conflict
Winston Tubman:
* Nephew of Liberia's longest-serving President William Tubman
* Harvard-trained lawyer
* Justice minister under Samuel Doe
* UN envoy to Somalia from 2002 to 2005
* Came fourth in 2005 election
* Running mate is ex-football star George Weah
Our reporter saw one body, and three or four other injured people who said they had been shot.
The UN confirmed two deaths, Reuters reports.
These are the first elections organised by Liberians since the 14-year conflict ended. The previous ones were run by the large UN peacekeeping mission, which still has some 8,000 troops in the country.
Our reporter says armed policemen stormed and closed down two radio stations on Monday night - King's FM, owned by Mr Tubman's running-mate, former football star George Weah, and Love FM, owned by opposition politician Benoni Urey, whose National Patriotic Party (NPP) is in alliance with the CDC.
Police also tried to close a third broadcaster, Power-FM/TV, our reporter says.
'Bad signal'
Mr Weah condemned the shooting of "unarmed protesters" and called for the elections to be postponed.
President Sirleaf won the first round last month but failed to pass the 50% threshold needed for outright victory.
Mr Tubman and the CDC say there was widespread vote-rigging - charges denied by the election commission.
Its interim chairperson, Elizabeth Nelson, urged people not to threaten stability.
"I call on all of you to put Liberia above self. This is the only place that we have to call home," she said.
Liberian riot police walk past a burning tyre during clashes with supporters of presidential challenger Winston Tubman in Monrovia November 7, 2011. Opposition reports of four deaths in Monday's protests have not been confirmed
"We must do everything possible to preserve the peace. As a registered voter, turn out and vote."
The US, EU and African Union have all condemned the opposition's decision to pull out of the run-off.
"It's a bad signal... political leaders must be prepared to win or lose," said former Ugandan Vice-President and head of the African Union observer mission Speciosa Wadira Kazibwe, according to the AFP news agency.
Prince Johnson, a former warlord who came third in the first round, has backed Mrs Sirleaf in the run-off.
