The incident occurred at about 9 am on June 20 in Hong Lien Village, Ky Van Commune, Ha Tinh Province, when a fire broke out in an acacia plantation.
Local authorities used loudspeaker systems to alert residents and mobilised hundreds of people to help contain the blaze.
At around 1 pm, after the fire had been brought under control, rescue teams discovered the bodies of Ho Van Lien, 58, and Nguyen Thi Minh Hoa, 54, several metres apart.
Preliminary investigations found that the couple had entered the forest earlier that morning to burn vegetation in preparation for land improvement and tree planting.
The fire later spread to a neighbouring acacia plantation owned by another household. The couple reportedly attempted to extinguish the flames but were unable to stop the fire from spreading.
Authorities believe the victims may have lost consciousness due to oxygen depletion caused by the intense blaze and were unable to escape.
"The fire may have become too large, causing the victims to suffer from a lack of oxygen and collapse before they could get out," a source familiar with the investigation said.
The fire destroyed approximately five hectares of acacia forest.
Ha Tinh Province has experienced a heatwave over the past three days, with temperatures ranging from 28 to 38 degrees Celsius. Several mountainous areas have been placed under high forest fire warnings.
Since the beginning of the summer, local authorities have recorded two other small-scale forest fires in the province.