Liberians said "yes" to amendments by President George Weah to reduce the head of state's term and allow dual citizenship, according to partial results for a third of the country's regions announced Tuesday.
At the same time, voters inflicted a serious setback on the ruling party in the senatorial vote held on the same day.
The opposition has won 15 out of 30 senate seats, including the one for Montserrado County, the most populous county in the country, which includes the capital Monrovia.
About 2.5 million voters were asked to vote on December 8 on eight constitutional amendments, including one reducing the presidential term from six to five years.
The National Elections Commission (NEC) said "yes" to all eight questions won in the five counties where the count was completed, out of 15 in Liberia.
In the Senate, of the seven counties fully counted, the opposition won four, compared with two for George Weah's Congress for Democratic Change (CDC) and one for an independent candidate, according to the NEC.
In George Weah's historic electoral stronghold, one of his fiercest opponents, Senator Darius Dillon, was re-elected with 61% of the vote, according to the electoral commission.
The vote was also a referendum on President Weah, who had raised high hopes in 2018 by coming to power in this West African country still marked by the civil war of 1989-2003 and the Ebola epidemic of 2014-2016.
He failed to turn the economy around and enthusiasm gave way to disenchantment. The main opposition parties had called for a boycott of the referendum.
Although Weah, 54, is still in his first term, his opponents fear he will take advantage of a constitutional amendment to argue that the law offers him a fresh start, as did his Guinean counterpart and neighbor Alpha Condé and Ivory Coast's Alassane Ouattara.