Police tore down the Occupy Oakland encampment, in part because they say it has become a public safety and health threat.

Oakland, California, officials had warned protesters to move out of Frank Ogawa Plaza over the weekend, says a CNN report. The order to vacate the plaza came on Saturday, a day after a "frequent resident" of the camp allegedly shot and killed another man, the report says.

The developments in Oakland come amid rising concern from city officials around the country that the protests drain resources and threaten public health, the report notes.

In Portland, Oregon, police in riot gear and protesters faced off Sunday after Mayor Sam Adams said that "a series of increased drug overdoses, ... an arsonist that used the camp as camouflage and almost a 20% increase in crime surrounding the encampment" prompted officers to act, says the report.

In Philadelphia, Mayor Michael Nutter was quoted as saying, "Occupy Philly has changed. We're seeing serious health and safety issues playing out on an almost daily basis. ... The people of Occupy Philly have also changed and their intentions have changed. And all of this is not good for Philadelphia."

Numerous reports of thefts and assaults in the encampment have been made, and 15 emergency medical runs were made between October 6 and November 11, he said.