MEXICO CITY (Reuters) – Former Mexico City mayor and ruling party candidate Claudia Sheinbaum holds a comfortable lead in the race for Mexico’s presidency, an opinion poll showed on Monday, days before campaigns for the June 2 vote officially kick off.

A Feb. 15-21 survey of 1,000 Mexicans by pollster Buendia & Marquez for newspaper El Universal gave Sheinbaum, who represents the ruling leftist National Regeneration Movement (MORENA), 59% support of support in a three-way race with her closest rivals.

Sheinbaum, 61, is a close ally of President Andres Manuel Lopez Obrador, whose approval ratings remain strong. Under Mexican law, presidents may only serve a single six-year term.

Opposition coalition candidate Xochitl Galvez trailed with 36%, while Jorge Alvarez, a little-known congressman representing the center-left Citizens Movement (MC) party, earned 5% support. The poll had a margin of error of plus or minus 3.5 percentage points.

When given the option, one in five voters polled said they had no preference in the race.

A little over half of all voters polled – 54% – said they had made up their minds over who they would vote for.

Mexico’s presidential campaign will formally begin on March 1, although candidates have effectively been on the campaign trail for months.

Alvarez joined the presidential race in January after his party’s candidate, Nuevo Leon Governor Samuel Garcia, dropped out.

If either Sheinbaum or Galvez are victorious in the June vote, they would be the first female president in Mexico’s history.

(Reporting by Brendan O’Boyle; Editing by Alistair Bell)