Tui has cancelled all beach holidays up to and including 14 May after the Foreign Office (FCO) updated its travel advice at the weekend to advise against all non-essential travel worldwide for an "indefinite" period.
Marella Cruise holidays travelling up to and including 31 May will also no longer operate, while Tui River Cruise operations, which had been due to launch last month, will now start on 26 November.
"We are constantly monitoring the situation and will start taking people on holiday again as soon as we are able to do so," said Tui.
"At this point in time, nobody can accurately predict when that will be, so for the time being we will keep a close eye on our programme and continue to amend and adapt timings in line with the latest global travel advice.
"We will update our customers as soon as we can of any changes to their holidays. We, like other travel companies, want to travel again as soon as we possibly can and will do so in line with government advice."
The operator said its customer service teams would contact everyone affected, but warned that due to changes in the way it is having to work owing to Covid-19, including closure of all its retail stores, the process may take longer than usual.
"We do understand this may be frustrating but we’d like to assure everyone that we will be in touch as soon as we can," said the firm, adding customers who booked via retail should wait to be contacted to discuss their options.