Northern Ireland’s coronavirus reproductive rate has reached around 1.6, the health department said.
The seven-day average for new cases has more than doubled in the last week.
This is partly due to increased testing.
The department said: “However community transmission has gone up and hospital admissions have also begun to rise, though remain at a low level.”
An additional eight people have tested positive, the health authorities said on Thursday.
The reproductive rate indicates how many other people are likely to be infected by one confirmed case.
If it rises above one the rate at which the virus spreads grows exponentially.
If it stays below one it is being suppressed.
Cases are occurring in communities across Northern IrelandDr Gerry Waldron
An analysis of all Covid-19 cases across Northern Ireland by the Public Health Agency (PHA) shows that since the start of contact tracing on May 24, a total of 11 clusters with five or more people have been identified.
Since July, the average number of close contacts linked to cases has more than doubled.
The rise may be attributed to the gradual easing of lock down measures, but may also be explained by relaxing of attitudes to social distancing, the PHA said.
Dr Gerry Waldron, head of health protection at the organisation, said: “Cases are occurring in communities across Northern Ireland.
“This is an important reminder that we must not become complacent, coronavirus remains in circulation, so each of us has a responsibility to take steps to help keep ourselves and those around us safe.”
No new deaths with Covid-19 have been reported in Northern Ireland, the Department of Health said on Thursday.
An additional eight people tested positive.
Dr Waldron added: “Our analysis of clusters to date has shown that they have been associated with both workplaces and in the community, such as domestic gatherings and in hospitality and sporting settings.”