SAN SALVADOR: El Salvadoran President Nayib Bukele was on course to win a super-majority in Congress in mid-term elections, a preliminary vote count showed on Monday, with his party and allies likely reducing once dominant rivals to a handful of legislative seats.

The president's New Ideas party plus its allies had some 70% of the vote with more than 90% of votes counted, likely enough to win at least two thirds of seats in Congress and greatly increase Bukele's power in the Central American nation.

"The citizens heeded the President's call to give him enough lawmakers to be able to govern without any opposition," said Eduardo Escobar, electoral expert and executive director of the non-governmental organization Citizen Action.

"The results give him a free rein to rule ... there is basically no decision that they cannot make," said Escobar.

Bukele has faced criticism from rights groups and foreign powers for what they see as autocratic leanings.

He has ignored Supreme Court rulings against his policies and once sent armed soldiers into Congress, where until now he has held only a few seats, to pressure the opposition to back a crime-fighting plan.

But he has maintained sky-high approval ratings during his first two years in office, with voters happy to see him belittle the right and left-wing parties who have ruled since the 1992 end of the civil war but have since faced widespread accusations of corruption.

He has lowered crime and increased cash payments to families during the pandemic.

The electoral authority said it will only reveal the distribution of seats after a final count in next few days, but the size of the victory strongly suggested Bukele had won at least 56 of the 84 seats in the unicameral legislature.

That will allow the ruling party and allies to choose, without negotiating, five supreme court judges and a new attorney general as well as enacting constitutional change.

The 39-year-old Bukele, one of the world's youngest leaders, won a landslide victory in 2019 on a pledge to root out corruption.

Slightly more than half of the 5.3 million eligible to cast ballots participated in the election to pick lawmakers and local officials.

Some election-watchers expressed concern that the lopsided results could undermine the country's institutions.

"It creates a democratic worry that we'll lose a balance of powers," political analyst Oscar Picardo told local television station TCS.

The final vote count is expected to begin by late Tuesday.