Mexico marked the Sept. 19 anniversaries of 2017 earthquakes that killed more than 500 people and a devastating 1985 temblor that left at least 9,500 dead.

President Andrés Manuel López Obrador presided over a ceremony Thursday in which the flag was raised to half-staff in memory of the victims.

Mexico still has rebuilt less than half the homes damaged or destroyed in 2017 by the magnitude 7.1 Sept. 19 earthquake and a magnitude 8.1 temblor on Sept. 7.

Soldiers hold a portion of a Mexican national flag as it is raised at half-staff during the 34th anniversary of the 1985 earthquake, in Mexico City, Thursday, Sept. 19, 2019. The 8.1-magnitude earthquake killed as many as 10,000 and left thousands homeless. The date also commemorates the 2017 earthquake that rattled the city killing hundreds. (AP PhotoMarco Ugarte)

Soldiers hold a portion of a Mexican national flag as it is raised at half-staff during the 34th anniversary of the 1985 earthquake, in Mexico City, Thursday, Sept. 19, 2019. The 8.1-magnitude earthquake killed as many as 10,000 and left thousands homeless. The date also commemorates the 2017 earthquake that rattled the city killing hundreds. (AP PhotoMarco Ugarte)

David Cervantes of the government housing and zoning office said that by the end of 2019, reconstruction efforts will have reached 41% of the estimated 200,000 homes affected by the quakes.

Progress has been quicker at public facilities like schools and hospitals, where about two-thirds of damages have been repaired or reconstructed.

"We think that next year we can conclude the bulk of the reconstruction process," Cervantes said.

Mexico's President Andres Manuel Lopez Obrador leads a ceremony marking the 34th anniversary of the 1985 earthquake, in Mexico City, Thursday, Sept. 19, 2019. The 8.1-magnitude earthquake killed as many as 10,000 and left thousands homeless. The date also commemorates the 2017 earthquake that rattled the city killing hundreds. (AP PhotoMarco Ugarte)

Mexico's President Andres Manuel Lopez Obrador leads a ceremony marking the 34th anniversary of the 1985 earthquake, in Mexico City, Thursday, Sept. 19, 2019. The 8.1-magnitude earthquake killed as many as 10,000 and left thousands homeless. The date also commemorates the 2017 earthquake that rattled the city killing hundreds. (AP PhotoMarco Ugarte)

He said some buildings, like old churches, might take longer, because their reconstruction process is often more complex.

The National Institute of History and Anthropology, which is responsible for historic sites, acknowledged the task was monumental.

"This is not work that you can do rapidly, given the kind of legacy buildings we are restoring with original materials and construction techniques," said Diego Prieto, the director of the Institute.

The Institute said it had completed work on 990 historic structures that were damaged, but that 1,350 still await restoration. That is a completion rate of about 42%. At some colonial-era churches experts are grappling with whether to restore some heavily damaged walls and vaults, or tear them down and rebuild them.