The chief executive of Tourism Ireland has said he has "extremely serious" concerns over the potential impact of coronavirus.
Niall Gibbons said there had already been trip cancellations, amid growing fears more visitors will stay away.
The first patient confirmed in the Republic of Ireland has been treated in a Dublin hospital.
The man from the eastern the main country was confirmed as having coronavirus on Saturday, RTE reported.
It followed a female from Northern Ireland being diagnosed with the virus on Thursday.
Both had travelled home from an affected area in Italy.
"The coronavirus story has moved from its first chapter, which happened in China, into its second chapter now and our concern has moved from very serious to extremely serious," Mr Gibbons told BBC Northern Ireland's Sunday Politics programme.
"What has happened in the last week is of a more serious nature.
"European people to the island of Ireland spend about €2bn (£1.7bn), it really is a big part of our income.
"Sixty-six per cent of European people to Northern Ireland come via the Republic of Ireland, so working together has never been more important.
"We are seeing no-shows, we are seeing cancellations in the last week."
Mr Gibbons also highlighted the cancellation of next week's international tourism fair ITB in Berlin, where 30 companies have been set to market the island of Ireland at the world's biggest trade show.
But he added that tourism across the island of Ireland was a "strong product" and would "bounce back".
Last month it had been warned that the tourism industry in Northern Ireland have been damaged by the outbreak, at a spot when it had been still largely confined to China.
Ireland's clash with Italy in the Six Nations rugby tournament has been called off and Mr Gibbons said he expected a decision on whether Dublin's St Patrick's festival from 13-17 March would just do it would be taken by the finish of the week.