"We have been alerted to large numbers of jellyfish in the Mediterranean this summer, especially in a number of key holiday destinations for United Kingdom tourists," a Foreign Office spokeswoman told BBC News.
"We have updated our travel advice for a number of Mediterranean countries to reflect this issue," she said.
While authorities have already warned of jellyfish in Mediterranean coastal waters off France and Italy, local marine biologists said this year's bloom was "no different" from other years and that they consisted of non-stinging species.
"Of course, as in any other ocean or sea in the world, there might be some problems," Stefano Piraino, project coordinator of the Mediterranean JellyRisk program, said. "In the Mediterranean, we are lucky and do not have deadly [jellyfish]."
Piraino acknowledged an increase in blooms.
"We are experiencing, as in many other places around the world, an increase in jellyfish," he said, adding it was difficult to identify a single cause for the increase in the numbers.
"This is a result of many different causes. These can be different from site to site," he said. "Generally, there is evidence that there is an increased abundance because of an increase in sea surface temperature."