Tehran: Iran's state TV says the number of people injured by a Thursday earthquake of moderate strength affecting the northeastern city of Neyshabour has increased to around 230.

The Friday report says 30 of the injured people were hospitalised, with the others treated for minor injuries and released. No deaths have yet been reported.

State TV reports that many residents of the city camped out overnight in subzero weather in streets and parks, fearing further tremors.

Since Thursday afternoon's magnitude 5.5 earthquake, some 75 aftershocks have jolted the city of 220,000 about 900km northeast of the capital Tehran.

Iran is located on seismic fault lines and is prone to earthquakes, experiencing at least one slight quake a day on average.