Authorities say a wildfire that ignited in Mexico has crossed the border and started burning in southern Arizona.
The La Sierra Fire, as it is called, was first observed Sunday as a column of smoke. Firefighters were moved into position to begin responding as soon as it crossed into the United States, which it did around 2:30 p.m. Monday into an area northwest of Nogales.
The fire has burned about 320 acres of the forest so far, generating a large amount of smoke that has drifted east to Rio Rico.
Two hotshot crews and an initial attack crew, 65 people in all, are already fighting the fire. Three helicopters have also been pulling water from Pena Blanca Lake. Officials said two more crews and four more engines had been ordered to the scene and would begin work on Tuesday.
Park officials asked visitors to avoid Pena Blanca Lake and Ruby Road while firefighters worked to contain the flame.