BANGKOK (AFP) - Thai police charged two executives of a fire safety company with negligence on Tuesday (March 15) after a malfunctioning extinguisher system killed eight people inside a Bangkok bank on Sunday.

The accident happened while contract workers were upgrading the chemical fire extinguisher system in the basement of the headquarters of Siam Commercial Bank, one of the country's largest financial institutions.

The bank said the contractors mistakenly set the system off, releasing a chemical retardant designed to starve any fire of oxygen.

Seven of those killed were contractors while the eighth victim was a bank security guard.

On Tuesday police charged two executives from Megaplanet, a company contracted by the bank that outsourced the work to a third outfit.

"Police explained the charge of negligence resulting in deaths to both suspects," said Bangkok's city police commander Sanit Mahathavorn.

The executives, Adisorn Phoka and Napong Suksa-nguan, could face up to 10 years in prison.

Sanit said police are still investigating how the system was triggered and why victims were seemingly unable to escape the thick cloud of chemicals.

Photos published by local media showed rescue workers battling a smoky haze to reach the victims, five of whom were killed at the scene.

Bodies were brought out wrapped in white blankets while paramedics could be seen trying to resuscitate victims on the pavement.

Seven injured are still receiving medical attention at a hospital, according to Bangkok's Erawan emergency medical centre.

The bank expressed sympathy for the victims in a statement on Monday and said the rest of the building was unaffected and operating normally.