Checks may be needed on the Irish border in the event of a no-deal Brexit, Leo Varadkar has warned.
The Irish premier outlined the impacts of the United Kingdom leaving the European Union without a deal during a speech to business leaders in Dublin.
He said there will be checks on goods and live animals, which he said would take place "as far as possible" in ports, airports and at businesses.
"But some may need to take place near the border," he said.
The Taoiseach said recent chaos in UK politics had led him to fear a "significant and growing risk of no-deal".
"We don't wish to see a no-deal Brexit and we will continue our efforts to avoid one, but not at any cost.
"Unlike some, I see no upsides to no-deal. I do fear it. But I am prepared for it."
The Taoiseach told a British Irish Chamber of Commerce dinner that his government is "working out the details" with the European Commission in terms of the impact of a no-deal Brexit.
He said the common travel area will remain in place, but outlined the changes he expects.
"There will still be plenty of food on shelves but perhaps not all of the same brands," he said.
"When you fly into Ireland from Britain, you will no longer pass through the blue channel.
"You will have to choose the green or red one and pay any taxes that may be due.
"The same will apply to products bought online from the UK, brought in from Northern Ireland, and EU consumer protections will no longer apply.
"Flights, trains and buses will continue to operate normally for a period but an agreement will be needed for this to continue permanently. EU vessels will no longer be allowed to fish in UK waters and vice versa, though the Commission has proposed a short extension of the status quo.
"Tariffs will apply to goods imported into Ireland from the United Kingdom and vice versa.
"There will be checks on goods and live animals and, as far as possible, they will take place in ports, airports and at businesses. But some may need to take place near the border.
"We are working out the details of this with the European Commission."
The Taoiseach added that whatever happens the UK will "remain a vital trading partner", noting billions of euros worth of exports and imports between the two nations in 2018.
"The UK is geographically and culturally our closest neighbour and will continue to be a vital trading partner, no matter what shape Brexit takes," he said.
SDLP leader Colum Eastwood said Mr Varadkar's comments "underscore the need for a backstop to prevent the re-emergence of a hard border in Ireland".
"Taoiseach Leo Varadkar has clearly laid out some of the immediate challenges border communities and businesses will face in the aftermath of a no-deal exit.
"It is uncomfortable listening for people who rely on frictionless travel and trade across this island," he said.
"The warnings issued this evening again underscore the critical need for a backstop to protect the interests of people, communities and businesses on this island."