Congo is holding its elections under a media blackout and the tense vote is expected to see President Denis Sassou Nguesso prolong his 32-year rule over the oil-rich but poor nation.

Interior Minister Raymond Mboulou wrote to telecommunication companies urging them to shut off telephone, internet and SMS services for 48 hours for "reasons of security and national safety".

A government source told AFP news agency the shutdown was intended to stop any "illegal" publication of the results of Sunday's elections.

Tensions have been running high in Congo since October, when a public referendum backed removing a two-term limit that would have kept 72-year-old former paratrooper colonel Sassou Nguesso from power.

The vote also removed a 70-year age limit for the presidency that could have forced one of Africa's five longest-serving leaders to step down.

The changes were approved in a referendum by 94.3 percent - dubbed "a constitutional coup" by the opposition - and protests erupted in the run-up to the vote that left several people dead.

The incumbent president has said he has no doubt he will beat his eight rivals, describing election day as a "penalty kick and then victory".

On Friday, five rival presidential contenders - including former military chief Jean-Marie Mokoko - signed an agreement to back the strongest candidate among them in the event of a second-round vote.

'Fears of instability'

While the Republic of Congo saw "robust growth" of 5 percent over five years through to 2014, with oil and timber providing its main revenues, the country remains in dire straits.

"[Congo] continues to suffer from high rates of poverty and inequality, large infrastructure gaps, and important development challenges," a report by the International Monetary Fund released in July 2015 said.

READ MORE: Congo holds referendum on presidential term limits

Unemployment hit 34 percent in 2013, the last data available, and stood at 60 percent for 15 to 24-year-olds.

The IMF fears "domestic instability" without progress in the battle to eliminate poverty.

"We're really disappointed about what's happening in Congo," said 20-year-old student Yette. "Most young people have diplomas but no work."

Sassou Nguesso admits there is a problem but has told voters he needs more time.

His new election platform underlines government efforts in education while noting that "60 percent of graduates without work" qualified at the country's sole university.

"Seven years were insufficient to fully make these solutions operational ... which is why we need to continue the country's modernisation and industrialisation," reads the new platform.

Sassou Nguesso served as president from 1979 to 1992 and returned to power in 1997 after a civil war.

He won two successive mandates in 2002 and 2009, but both tallies were contested by opposition parties.