Nokia, BT, Vodafone and Deutsche Telekom are the latest companies to pull out of the Mobile World Congress (MWC) trade show, citing concerns about the new coronavirus.
Organiser GSMA is holding urgent talks about whether to cancel the event, with an announcement expected later.
Barcelona's Mayor, Ada Colau, sent "a message of calm", saying the city was ready to host the event.
And health officials said there was no need to declare a health emergency.
At a press conference in the city, Spain's Minister of Health, Salvador Illa, urged people to remain calm, "trust in the Spanish health system" and "take decisions based on scientific evidence".
Earlier this week Amazon, Sony, LG Electronics, Ericsson, Facebook, and chipmakers Intel and Nvidia said they would not attend the conference, scheduled for 24-27 February.
French telecoms group Orange will also be a no-show, despite the fact its chief executive, Stephane Richard, chairs the GSMA.
A report in Wired suggests insurance policies would not cover losses if GSMA chooses to cancel the event, rather than being required to do so by authorities declaring a health emergency.
More than 100,000 people usually attend the annual event, about 6,000 of whom travel from China, and thousands of companies exhibit, giving a huge lift to the Spanish economy.
"To bring people together and connect them - that is what Telekom stands for. This is also what the Mobile World Congress, the 'class reunion' of our industry, stands for," Deutsche Telekom chief executive Tim Hoettges posted on LinkedIn.
But large gatherings with many international guests posed a particular risk, he said, adding: "To take this risk would be irresponsible."
China's top smartphone manufacturer, Huawei, and its smaller rival ZTE said their plans remained unchanged.