Ms Sheinbaum, a scientist

Ms Sheinbaum, a scientist who ran Mexico City in 2018-23, has the backing of the outgoing president, Andrés Manuel López Obrador.

Mario Delgado, the president of Mr López Obrador's party, called her expected victory a "stellar moment in the history of our country".

Mr López Obrador, who has been in power since 2018, cannot run for the top office again, as under Mexico's constitution, presidents are limited to a single six-year-term.

The popular leader - recent polls suggested he had an approval rate of close to 60% - has instead thrown his weight behind Ms Sheinbaum, who is part of his Morena party.

While many of the promises President López Obrador made upon taking office have remained unfulfilled, his efforts to reduce poverty and help elderly Mexicans have been popular with beneficiaries of these social programmes.

Having the backing of the president may have considerably widened Ms Sheinbaum's base of voters, but it has also raised questions about how independent she is of the sometimes overpowering leader.

Ms Sheinbaum has stressed that she is very much her own woman, while at the same time promising to continue building on what she says are Mr López Obrador's many achievements.

Their party boasts about how millions of Mexicans have been lifted out of poverty during the past six years.

Morena says the number of people living in poverty is dwindling thanks to its policies, such as more than doubling the minimum wage.

But economists have pointed out that there are also other factors at play, such as a rise in remittances being sent by Mexicans living abroad to their friends and family at home.