Coronavirus infections in Italy rose 50% Sunday and the U.S. government issued its strongest travel warning yet, advising Americans against any travel to two regions in northern Italy that have been hard hit by the virus that first emerged in China in December.

Authorities said the total number of people infected in Italy had risen to 1,694, a 50% jump from just 24 hours earlier. Five more people infected with the virus have died, bringing the deaths in Italy to 34, while 83 people have fully recovered, the UNB reported.

Italian health authorities said the increases were expected, since it takes as long as two weeks for containment measures to take effect, and because Italy has a large number of elderly people. Still, the numbers highlighted the rapid impact the virus is having on Italy, the epicentre of the outbreak in Europe.

''This acceleration was expected, unfortunately,'' said Giovanni Rezza, director of the infective illness department at the National Health Institute. He said it would be another week or 10 days until the spread of the virus slowed down in the country.

With numerous cases in other European countries traced back to Italy, many countries have issued travel warnings for the 11 Italian towns that have been on lockdown since the virus exploded there on Feb. 21. But none have gone as far as the U.S. government, which on Sunday urged Americans not to travel to the regions of Lombardy and Veneto, raising the warning to the highest level. It is one step shy of the U.S. travel advisory for China, which urged Americans to leave the country.

In the wake of the warning, Delta and American Airlines have both suspended flights to Italy's financial capital of Milan, which can have a potentially devastating business impact beyond just tourism. Already a major furniture and design fair has been postponed due to the virus until June.

Tourism officials said an earlier U.S. travel warning covering all of Italy was potentially calamitous to the industry, which represents 13% of gross domestic product in a country famed for its world-class museums, archaeological sites, art cities and natural beauty.

More than 5.6 million Americans visit Italy every year, representing 9% of foreign tourists and the second-largest national group behind Germans, according to the most recent statistics.

China accounts for the vast majority  of the 88,000 people infected by the virus and the 3,000 killed by it.

Lombardy, which includes Milan, accounts for over half of the cases while Veneto and Emilia-Romagna have 15% and 17%, respectively. All three regions have closed schools for at least another week. In Veneto and Lombardy, closures also have hit museums, theaters, cinemas and most public offices, emptying cities like Milan, where many companies have permitted office workers to telecommute.

Earlier Sunday, the French community church in Rome, St. Louis of the French, closed its doors to the public after a priest was infected with the new virus.

The church in the historic centre of Rome is famous for three paintings by the Baroque master Caravaggio, making it a destination for tourists and the faithful alike. A sign on the door Sunday noted in French that the church had been closed as a precaution by the French Embassy for both Masses and tourist visits until further notice.

The Religious Information Service news agency reported the church was closed after a 43-year-old priest who had returned to Paris was hospitalized after being infected. It carried a statement by the archbishop of Paris, Michel Aupetit, who said the priest, who had been living in Rome, returned to Paris by car in mid-February and tested positive for the virus on Friday. He was in good condition, Aupetit said.

It was the first church in Rome closed by the virus. Churches in much of Veneto and Lombardy have closed their doors under widespread measures aimed at containing the spread of the virus. Televised Masses have been available for the faithful.