The longtime leader in Republic of Congo is expecting an easy election day victory after the country's constitution was changed so he could run again.

President Denis Sassou N'Guesso, 72, was barred from seeking re-election until the October referendum removed term and age limits.

Sassou N'Guesso first became president in 1979, remaining in office until he lost the country's first multi-party election in 1992. He returned to power in 1997 after his rebel forces ousted the president.

The run-up to the referendum was marred by violence which the president's critics denounced as a "constitutional coup."

Officials have closed the country's land borders for Sunday's vote and only emergency vehicles will be allowed on the roads. The government has ordered telecommunications services to be blocked on Sunday and Monday.