Mexican authorities have found the remains of 42 people in a vacant lot in the northern border state of Sonora, a group dedicated to finding missing people said on Tuesday.

"That was the last we could find, they've stopped us from searching because there have been a lot of bodies," said Ceci Flores, the leader of Madres Buscadoras de Sonora, a group of mothers in Sonora trying to locate missing loved ones.

The skeletons of 40 people and two recent corpses were discovered by officials and the mothers' group during searches for missing people near the resort town of Puerto Penasco, the attorney general's office for Sonora said in a statement.

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.

Partial view of the beach in Puerto Penasco, Sonora state, Mexico. Officials have recovered the remains of 42 people from a vacant lot in the town. (Pedro Pardo/AFP/Getty Images)

Clothes found at the site suggested that only two of the sets of remains likely belonged to women, the statement added.

Flores said her group would search for more remains at the site, some 8 kilometres from Puerto Penasco, once investigators had conducted examinations on the bodies found.

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