Witnesses said smoke was seen billowing from the building, drawing the attention of members of the public and businesses within the mall.
Some occupants were evacuated as a precautionary measure while emergency teams moved in to manage the situation.
The Kenya Red Cross confirmed that the cause of the fire remains unknown at this stage.
Authorities are expected to conduct investigations once the situation is fully brought under control to determine what may have triggered the incident.
Firefighters have been working to contain the flames and secure the area, with support from other emergency agencies.
Their priority has been to ensure the safety of people in and around the premises, as well as to minimise damage to property.
The incident has caused temporary disruption to activities at Highway Mall, with access to some sections of the facility restricted to allow emergency operations to continue.
Officials have urged members of the public to keep away from the affected area to allow responders adequate space to carry out their work.
They have also called for calm, noting that the situation is being handled.
While no injuries or fatalities have been reported, the extent of damage to the building and property is yet to be determined.
Business owners and tenants within the mall are expected to assess any losses once the fire is fully extinguished and the area declared safe.
The Kenya Red Cross said it will continue to monitor the situation and provide updates as more information becomes available.
Authorities are also expected to release further details after preliminary assessments are completed.