MEXICO CITY - 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 Andres Manuel Lopez Obrador presided over a ceremony Thursday in which the flag was raised to half-staff in memory of the victims.

While Mexico City has earthquake alarms and regular evacuation drills, the city remains far from ready: 26 people were injured from sprains, panic attacks or fainting spells during Thursday's drills.

Meanwhile, the alarms give only about 50 seconds warning of quakes, most of which are centred on the Pacific coast, and thousands of buildings and houses damaged in the 2017 quake have yet to be reinforced or rebuilt.

Nationwide, Mexico 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.

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.

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.