Seismological sources from Shillong said the earthquake with epicentre at Nagaon's Katiaholi and Puronigodam alongside the hills of Karbi Anglong district occurred at 6.11 pm.
Official sources said two labourers sustained serious injuries in the wall collapse while they were on working at Raha in Nagaon. They were admitted to Nagaon civil hospital and reported to be out of danger.
A mosque near the Sadar police station in Nagaon and several buildings were damaged in the impact of the tremor that lasted nearly five seconds.
A concrete wall collapsed in the Jyotinagar while cracks occurred in a multi-storeyed building in the Beltola area of the city.
Some temporary huts were also damaged in the slum areas of the city.