A popular candidate running for Ecuador's presidency was shot dead as he was leaving a rally in the capital Quito on Wednesday evening, officials said.

President Guillermo Lasso blamed Fernando Villavicencio's death on "organized crime" in a statement on X, formerly known as Twitter, and vowed to bring the perpetrators to justice.

"Outraged and shocked by the assassination of presidential candidate Fernando Villavicencio," he said. "For his memory and for his fight, I assure you that this crime will not go unpunished."

The 59-year-old centrist, who had complained of receiving threats against him, was the second most popular candidate in the country's August 20 presidential race, according to recent opinion polls.

Villavicencio was murdered as he was leaving a stadium in northern Quito after holding a campaign rally, officials said.

Nine other people were injured in the attack, including a candidate running for the national legislature and two policemen, prosecutors said.

One of the alleged attackers was shot and killed by security personnel. And police detonated an explosive device planted in the area, said chief investigator Alain Luna.

Carlos Figueroa, a friend of Villavicencio's who was with him at the time of the attack, told local media that the assailants fired around 30 shots.

"They ambushed him outside" the sports center, Figueroa said. "Some (of those present) even thought they were fireworks."

The country's main newspaper, El Universo, reported that Villavicencio was assassinated "hitman-style and with three shots to the head."

- 'Full weight of the law' -

In recent years, Ecuador has been hit by a wave of violence linked to drug trafficking which, in the midst of the electoral process, has already led to the death of a mayor and a parliamentary candidate.

The homicide rate doubled between 2021 and 2022.

Lasso summoned top security officials for an urgent meeting on "this event that has shocked the country."

"Organized crime has gone too far, but the full weight of the law will be applied to them," Lasso said in his post.

According to the latest polls, Villavicencio, a former journalist who wrote about corruption and served in parliament, polled at 13 percent behind lawyer Luisa Gonzalez, who is close to former left-wing president Rafael Correa.

Gonzalez and other presidential candidates denounced the murder and said they were suspending their campaigns, local media reported.

National Court of Justice president Ivan Saquicela called Villavicencio's murder "very painful for the country."

"I am very hurt and very worried about Ecuador," he said.

Villavicencio had complained this month that he and his team were receiving threats allegedly coming from the leader of a criminal gang linked to drug trafficking.

"Despite the new threats, we will continue fighting for the brave people of our #Ecuador," he posted on X at the time.

The president of the National Electoral Council (CNE), Diana Atamaint, also said that several members of her organization, which is responsible for supervising the ballot, had received death threats.

Lasso sent a message to Villavicencio's family.

"My solidarity and my condolences with his wife and his daughters," he said in his post.