Hundreds of police in riot gear have dismantled the Occupy Oakland camp, evicting and arresting protesters in the second such US move in as many days.

Several people gathering for a prayer service at the site were arrested, as were some protesters who remained in their tents during the operation.

Yesterday, police evicted dozens of anti-Wall Street protesters from downtown Portland, Oregon in the western United States, making over 50 arrests in one of the latest cities to act against the encampments.

The police interventions could be seen as a turning point of sorts, after three deaths last week at Occupy camps, including a deadly shooting at the Oakland site, rocked the movement.

The Oakland camp, part of the Occupy Wall Street movement that began in September in New York, and whose protests against corporate greed, corruption and growing wealth gaps have gone global, has been a point of controversy for weeks.

When a man was fatally shot near the camp Thursday, apparently after a dispute, city officials concluded it was time to act.

Following the shooting, Oakland Mayor Jean Quan was quoted by the LA Times as saying that the camp would have to be closed down.

"Tonight's incident underscores the reason why the encampment must end," she said.

Protesters had kept dozens of tents at the site, defying several police orders to leave last week.

Earlier this month more than 80 people were arrested and eight injured in Oakland clashes following a day of anti-Wall Street protests and strike action.

In Burlington, Vermont, a man was found dead in his tent last week from a gunshot which the Burlington Free Press newspaper reported may have been self-inflicted. Tensions rose at the camp when armed police ordered protesters out while the investigation unfolded.

There was another death last Tuesday, at the Occupy New Orleans site, where a dead man was found in his tent at the encampment across from City Hall.

Local news reports quoted the coroner's office saying the 53-year-old man, who showed no signs of trauma, appeared to have been dead for at least two days before he was discovered.

While there has been mixed public reaction to the ragtag but enthusiastic Occupy Wall Street movement and its affiliates, the official tone has soured in at least one more major city were the protesters have gathered.

"Occupy Philly has changed," Philadelphia Mayor Michael Nutter told reporters on Sunday, citing "dramatically deteriorating conditions" at the site including a change in the people in the camp, and increased reports of theft.

"We're seeing serious health and safety issues playing out on almost a daily basis," he said, adding that on Saturday a woman reported an alleged sexual assault in one of the tents.