A 4.2-magnitude earthquake which struck off the NSW mid north coast is part of a "swarm" of small tremors that have shaken the region in less than a week.

The quake hit just before 1.30pm on Wednesday near Nambucca Heads, with small seismic activity continuing in the area.

Red dots representing locations where people have reported feeling the earthquakes. Credit:Google Earth

Geoscience Australia said the quake could be felt as far south as Port Macquarie, north to Coffs Harbour and inland to Armidale.

While there was no tsunami threat to Australia, the quake could have caused damage up to 6km away from its epicentre.