The coronavirus R rate in Northern Ireland could be as high as 1.8, officials have said.
The regional government's health department said on Thursday that the rate had risen from between 0.5 to 1 last week to between 0.8 and 1.8 this week.
R represents the number of individuals who, on average, will be infected by a person with the virus.
A spokeswoman for the Department of Health said while community transmission remains low in Northern Ireland, the number of positive tests per day has increased three-fold from early July.
Chief scientific adviser Professor Ian Young said: “The most recent data for Northern Ireland underlines the need for continued vigilance.
“There are five key steps each of us can take to keep ourselves and others safe – rigorously maintain social distancing; wash our hands well and often; wear face coverings in enclosed spaces where social distancing is difficult; co-operate fully with the Test, Trace and Protect programme, and download the Stop Covid NI app.”
The reported uptick in the R rate came as Northern Ireland reported 43 more Covid-19 infections in the region, bringing the total to date to 6,049.
However, no new deaths were recorded on Thursday, leaving the total in the region at 556, according to official figures.