Chile reported 15 new cases of swine flu on Friday, hours after Argentine protesters stoned a bus with Chileans suspected of carrying the virus and police fired rubber bullets to disperse the mob.
"The Institute of Public Health has confirmed 44 cases of A(H1N1) flu in Chile," officials said, upping the total by 15.
Chile has the largest number of recorded cases in South America.
On Thursday, police in the Argentine border state of Mendoza fired into the air to disperse a crowd that had attacked a bus with tourists whom they suspected were carrying the disease.
Residents of the town of Godoy Cruz were trying to stop the 43 passengers, one of whom had flu-like symptoms, from reaching a local hospital where they were required to appear. That prompted the Chilean interior minister, Patricio Rosende, to call for calm: "There is no reason whatever for the kind of hysteria that has been seen in some areas over the presence of a person who is possibly affected," he said.
Argentina, which soon faces legislative elections, was among the first countries to suspend flights to and from Mexico after the outbreak of the disease.
But on Friday authorities in Buenos Aires said it would not close the border with its western neighbor, despite the spike in cases here.
Two swine flu cases have so far been confirmed in Argentina.