Closing Northern Ireland to travellers from the rest of the UK would have serious ramifications, the First Minister said.
The new strain of coronavirus has probably already arrived, Arlene Foster added, but warned against threatening supply chains in response.
She said ministers were very concerned about the highly infectious mutation and tests were ongoing.
The DUP leader added: “It is a very simplistic thing to say, ‘let’s close Northern Ireland off’.
“That has ramifications and as First Minister I have to take all those into account as well.
“I have always tried to be proportionate and balanced in everything that I have done through this crisis, and I am going to continue to do that.”
The Stormont Executive is due to meet on Tuesday morning to discuss its pandemic response.
Sinn Féin has urged its powersharing partners the DUP to agree to an immediate response and expressed concern over flights arriving on Monday into the North.
Ms Foster said she was awaiting advice from Northern Ireland’s attorney general and more guidance from health officials.
She told UTV: “It is very important that we hear the public health advice on all of this.”
She said she was awaiting a paper from Health Minister Robin Swann indicating the risk posed by people travelling into the North.
Those in the highest level of restriction in England, Tier 4, are already barred from travelling to Northern Ireland.
She said she understood the risk posed by travelling was “small in nature” compared to other matters and warned supply chains could be affected.
“If it is small we have to level that up against the proportionality argument, in other words, what harm is it going to do if we stop people travelling into Northern Ireland,” she added.
