Mexican President Andres Manuel Lopez Obrador's party lost its absolute majority in the lower house in elections Sunday, initial results indicated, marking a setback to his promised "transformation" of the country.

The vote was seen as a referendum on his more than two years in office overshadowed by the coronavirus pandemic and cartel-related violence.

Dozens of politicians have been murdered in the months leading up to the polls for the lower house of Congress, 15 of 32 state governors and thousands of local politicians.

Current composition of the Mexican Chamber of Deputies by parliamentary group Current composition of the Mexican Chamber of Deputies by parliamentary group Photo: AFP / Nicolas RAMALLO

On the eve of the elections, gunmen killed five people helping to organize voting in southern Mexico, while two human heads were left at polling stations in the border city of Tijuana on election day.

Early results suggested Lopez Obrador's Morena party was set to take between 190 and 203 of the 500 seats, the National Electoral Institute said, though it could still secure an absolute majority with its allies.

The ruling coalition has had a two-thirds supermajority in the lower house of Congress that enabled Lopez Obrador to amend the constitution without negotiating with his opponents.

Mexicans will elect 500 members of the lower house of Congress as well as 15 state governors and thousands of local politicians Mexicans will elect 500 members of the lower house of Congress as well as 15 state governors and thousands of local politicians Photo: AFP / Alfredo ESTRELLA

Without it, he faces a tougher time pushing through his planned reforms, including seeking greater energy independence for Mexico.

"It's a defeat for Lopez Obrador -- not overwhelming -- but it does weaken him and his project because it requires constitutional reforms," said political analyst Jose Antonio Crespo.

"It's an important victory for the opposition because it was able to capitalize on the discontent, although the reality is that people voted against Lopez Obrador, not for his opponents," he told AFP.

Mexican President Andres Manuel Lopez Obrador enjoys public approval ratings above 60 percent Mexican President Andres Manuel Lopez Obrador enjoys public approval ratings above 60 percent Photo: AFP / PEDRO PARDO

A coalition of three opposition parties was set to increase its number of lower house seats to between 181 and 213, the National Electoral Institute said.

Mexicans will vote in elections seen as critical to President Andres Manuel Lopez Obrador's reform agenda Mexicans will vote in elections seen as critical to President Andres Manuel Lopez Obrador's reform agenda Photo: AFP / PEDRO PARDO

That would still be behind Morena and its allies, which were projected to control 265-298 seats.

Lopez Obrador was elected in 2018 for a term of six years, vowing to overhaul Mexico's "neoliberal" economic model, root out corruption and end profligacy by a privileged elite.

But his presidency has been largely dominated by the coronavirus pandemic, which has left more than a quarter of a million people dead in Mexico and devastated the economy.

Mexicans wait to cast their votes in San Bartolome Quialana in the southern state of Oaxaca Mexicans wait to cast their votes in San Bartolome Quialana in the southern state of Oaxaca Photo: AFP / PATRICIA CASTELLANOS

While the 67-year-old president himself continues to enjoy public approval ratings above 60 percent, Mexican voters often use midterm elections to punish the ruling party.

"They never had a plan and they still don't," said Claudia Cervantes, a hospital worker, said of the government's handling of the crisis.

But some other voters such as Tania Calderon were willing to give Morena more time.

"Without the pandemic, the government would have done better," the 37-year-old said.

Mexico's economy, the second-largest in Latin America, plunged by 8.5 percent in 2020 in the worst slump in decades, although the government predicts a rebound this year.

Lopez Obrador owes much of his popularity to his social welfare programs aimed at helping the elderly and disadvantaged Mexicans.

His supporters say he is their first president to put the interests of the Mexican majority, many of whom live in poverty, before those of the wealthy elite.

The president's critics accuse him of a dangerous tilt towards authoritarianism with attacks on the judiciary and the National Electoral Institute.

"Long live democracy," Lopez Obrador declared Sunday after voting.

The vote has been overshadowed by a wave of political bloodshed that has seen more than 90 politicians murdered since the electoral process began in September.

In the southern state of Chiapas, gunmen killed five people on Saturday in an attack that coincided with the delivery of ballot boxes and other voting materials.

In Guerrero, one of the country's most violent regions, also located in southern Mexico, members of a community police force kept watch over voting.

"Members of organized crime come to divide the people. They don't let them vote freely," said community police leader Isaias Posotema.