MEXICO CITY — It might have been any other day in El Salvador, but as the hours ticked into evening it became notable not for what happened, but for what didn’t.

An entire day had passed without a single murder in one of the world’s most violent places.

There was no particular reason the count was zero on Wednesday, Howard Cotto, the director of the National Civil Police, told local reporters the next day. Indeed, the police had registered 99 murders in the first 10 days of 2017 — an average of almost 10 a day.

Gang violence in El Salvador, an impoverished Central American country of 6.5 million, has given it one of the highest murder rates of any nation that is not at war. Youth gangs battle one another over extortion rackets that extend to the smallest of businesses, and no one seems to be immune from the bloodshed, which is also exacting a toll on the police.

Mr. Cotto noted that violence began to decline last year, which ended with 5,278 murders. Although the average was more than 14 a day, it was still 20 percent fewer than in 2015.