CODOGNO, Italy >> Scrambling to contain rapidly rising number of new coronavirus infections in Italy, the largest amount outside Asia, authorities today stepped up measures to ban public gatherings, including stopping Venice’s famed carnival events, which have drawn tens of thousands of revelers to a region that is now in the heart of the outbreak.

“The ordinance is immediately operative and will go into effect at midnight,” announced Veneto regional Gov. Luca Zaia, whose area includes Venice, where thousands packed St. Mark’s Square to join in carnival fun. Carnival, would have run through Tuesday. Buses, trains and other forms of public transport — including boats in Venice — were being disinfected, Zaia told reporters.Museums were also ordered to shut down after Sunday in Venice, a top tourist draw anytime of the year.

Authorities said three people in Venice have tested positive for the COVID-19 virus, all of them in their late 80s and who are hospitalized in critical condition. Zaia said among those infected was a nurse.

Nearly all of Italy’s 133 known cases are clustered in the north, at least 25 of them in the Veneto region.

Authorities expressed frustration they haven’t been able to track down the source of the virus spread in the north, which surfaced last week when an Italian man in Codogno in his late 30s became critically ill.

“The health officials haven’t been yet able to pinpoint Patient Zero,” Angelo Borrelli, head of the national Civil Protection agency, told reporters in Rome.

At first, it was widely presumed that the man was infected by an Italian friend he dined with and who recently returned from his job, based in Shanghai. When the friend tested negative for the virus, attention turned to several Chinese who live in town and who frequent the same cafe visited by the stricken man. But Lombardy Gov. Attilio Fontana told reporters all of those Chinese have tested negative, too.

So for now, Borrelli indicated, strategy is concentrating on closures and other restrictions to try to stem the spread in the country which already had taken such measures early on in the global virus alarm, including banning direct flights from China, Hong Kong, Taiwan and Macau. Italy has also tested millions of airport passengers arriving from other places for any sign of fever.

In Lombardy, with 90 cases, so far the hardest-hit region, schools and universities were ordered to stay closed in the coming days, and sporting events were canceled. Lombardy’s ban on public events also extended to Masses in churches in the predominantly Roman Catholic nation.

But while public Masses were forbidden in some towns in the hardest-hit areas, in the south, thousands turned out in the port city of Bari for a Mass by visiting Pope Francis, who shook hands with the faithful during his public appearance.Among those shaking the pope’s hand in Bari was Italian President Sergio Mattarella, who came to Bari for the event.

Museums, schools, universities and other public venues will be shut as well in Venice and the rest of Veneto. The shutdown is expected to last at least through March 1.

In Turin, the main city of the northern Piedmont region, a least three cases were diagnosed. That region also announced closure of all schools and universities.

The biggest jump in cases of confirmed COVID-19 was reported by authorities in Lombardy, a populous region which includes the country’s financial capital, Milan. Nearly all the cases were in the countryside, mainly in Codogno and nine neighboring towns, where only grocery stores and pharmacies were apparently allowed to stay open while other businesses were ordered shuttered and people — in theory at least — weren’t supposed to enter or leave the towns.

Melissa Catanacci, who lives on one of Codogno’s main roads, said that while entry points were open, others were closed.

Speaking by telephone from her home, she said she ventured outside for a stroll in the morning along with her husband and two children, ages 10 and 13.

“Every quarter-hour or so a car goes by” on the main road, she said. With businesses closed, the usual Sunday “passeggiata” — a leisurely stroll through local streets — didn’t last very long, she said. “Nothing is open,” not even the town supermarket despite permission to do so, she said. “After a half hour, one turns around and goes back home.”

With school to stay shut through the week, her children were visiting other friends’ houses and vice versa, she said, to break the boredom. For Catanacci, there was no reason to be overly concerned. COVID-19 is “a new virus, it’s still unknown to our body” and its antibodies, Catanacci said, adding: “it’s similar to influenza.”

Italians’ other cherished Sunday routines — from soccer to church-going — were being touched by the spread of the contagion, almost entirely based in the north. Sports events in the affected northern areas, including local kids’ sports team practices to three Serie A soccer matches, were canceled following a long meeting Saturday night by the Italian government to decide infection-containing measures.

Italy’s explosion of infections was sparking concern elsewhere on the European continent.

Austria’s top security official, Franz Lang said that the country could activate border controls to Italy within one hour. Normally both countries are part of the visa and passport-free Schengen zone, but in specific situations, single countries can reactivate border controls. Lang said the situation on the border and possible reactions to the virus outbreak would be discussed in meetings Monday, local Austrian media reported.

Italian Premier Giuseppe Conte on Saturday night said for now Italy wasn’t suspending Schengen zone rules.

In Switzerland, which, like Austria, borders Italy, there was a call for calm. Daniel Koch, the head of the department for contagious diseases at the heath office, told SRF public broadcaster that the country had not been contacted regarding possibly infected persons traveling to Switzerland and that there was no need to change the current strategy.

“The news from Italy are worrisome … but it is too early to think that a wave is rolling our way,” Koch said.

German travelers returning from northern Italy were being asked to check the official German health advisories online regarding possible exposure to the virus. The German health ministry said it had initiated a phone conference for all European Union public health authorities about the outbreak in northern Italy on Monday.

Italy’s first cases — that of a married Chinese couple who were on vacation in Rome — surfaced in early February.

To date, two deaths — of elderly persons in the north — have been reported among the 133 cases.

Elsewhere in Europe, French Health Minister Olivier Veran said that authorities were getting ready for a possible outbreak in France of the new virus. In an interview published today in French newspaper Le Parisien, he said he was monitoring very closely the “very serious” situation, including in neighboring Italy.

France reported earlier this month the first death outside Asia of a person infected with the virus, an 80-year-old Chinese tourist.