Mexican authorities have found the remains of 42 people in a vacant lot in the northern border state of Sonora, according to a group of mothers trying to find missing loved ones.

The skeletons of 40 people and two recent corpses were discovered by officials and the mothers group, Madres Buscadoras de Sonora, near the resort town of Puerto Penasco.

Leader Ceci Flores, who has been looking for one of her sons for four years, formed the group in May when a second son went missing.

Officials are working to establish the identities and the causes of death.

Thousands of people have disappeared in Mexico during a surge in gang-related violence during the last few years, and the find is another reminder of the task facing President Andres Manuel Lopez Obrador, who has pledged to pacify the country.

Meanwhile, the mayor of a Mexico City suburb was shot by two men on Tuesday (local time) and is in a serious condition.

Four Mexican mayors have been killed up to September this year - while eight were killed last year.

Reuters