Bogota, May 21 (IANS): Colombia's presidential race is likely to head to a runoff between progressive candidate Gustavo Petro and his conservative rival Federico Gutierrez, according to a poll.

Just over a week before the May 29 presidential elections, a survey by polling firm Invamer showed Petro has taken the lead with 40.6 per cent of the voter support, followed by Gutierrez with 27.1 per cent, reports Xinhua news agency.

Another conservative candidate, Rodolfo Hernandez, appeared to be gaining strength, with 20.9 per cent of the support, Xinhua news agency quoted the survey as saying.

A candidate must garner 50 per cent of the vote to win the first round, pointing to a likely runoff, said Martin Orozco, head of Invamer.

"With 40.6 per cent, Gustavo Petro is moving away from the possibility of winning in the first round, because we would have to get another 10 per cent against the two relatively strong candidates," Orozco said.

"There is an important conclusion: if the elections were today, then the runoff would be between Petro and Gutierrez. But in the survey we released 15 days ago, Hernandez was at 14 per cent and now he is at 21 per cent. That's seven more points."

A runoff will be held on June 19, and the winner will succeed incumbent President Ivan Duque on August 7.