Nicaraguans were expected to send President Daniel Ortega to his third term in office in Sunday's election, while some international observers said they were prevented from doing their jobs.

Polls closed at 6 p.m. local time with international election observers reporting problems with access to voting stations and with one national group of election observers, Let's Have Democracy, reporting 600 complaints of voting irregularities, a handful of injuries in protests and 30 arrests.

The head of the Organization of American States observer mission, Dante Caputo, said its observers have been denied access to 10 polling stations, which would account for 20 per cent of the statistical material they had planned to collect for their analysis.

Election observers from the European Union, said they were initially unable to monitor polls but were eventually allowed access.

The 65-year-old Ortega, once a Sandinista revolutionary, was leading his closest rival, opposition radio station owner Fabio Gadea of the Liberal Independent Party, by 18 points in the most recent poll.

Critics warn a third mandate could allow Ortega to seize the presidency for life.

Ortega is believed to command nearly 50 per cent of voter support in one of the poorest countries in the western hemisphere, and is riding on a populist platform as well as praise from the World Bank for his "broadly favourable" economic strategies.

The stage was set for Ortega to get back on the ballot when the Supreme Electoral Council, a division of the Supreme Court dominated by Sandinista judges, overruled the presidential term limits set by the country's constitution.

Critics of Ortega's candidacy have said that the elections are a sham and may be ushering in a new dictatorship after more than two decades of democracy. According to analysts, he could end up with a mandate that would not only legitimize his re-election but allow him to make constitutional changes guaranteeing perpetual re-election.

40% live on less than $2 a day

A third candidate and also former president, Arnoldo Aleman, had 11 per cent support in the recent poll, taken between Oct. 10-17 and with a margin of error of 2.8 percentage points.

Since he returned to power in 2007, Ortega has boosted his popularity with a combination of populism and a period of economic prosperity in a country of 5.8 million people, 40 per cent of whom live on less than $2 a day.

Viewed as a Soviet-backed threat by the U.S. during the Cold War, Ortega led the Sandinista movement that overthrew Anastasio Somoza in 1979, and fended off illegal U.S. government efforts to oust him through a rebel force called the Contras.

Ortega ruled through a junta before he was elected in 1984 but was defeated after one term in 1990. After two more failed runs, he softened his rhetoric, took a free-market stance, and regained the presidency in the 2006 election.

While Ortega has maintained close ties to the U.S., he is also being watched for what has been regarded as a close relationship with Venezuela's socialist President Hugo Chavez. He has been helped immensely by Chavez, who according to estimates has provided at least $500 million a year in discounted oil and outright donations.

With files from The Associated Press