New Orleans police officers are moving through the Hurricane Katrina (search)-devastated city and trying to get thousands of residents who have resisted moving to leave, a deputy police chief said Monday.

During a news conference, Deputy Superintendent Warren Riley said police were telling the remaining residents that there is no food, water or jobs and nothing to remain in New Orleans for.

"This city has been destroyed," Riley said.

Riley said police did have the authority to force evacuations, but did not spell out whether officers are taking that step. In an earlier interview on WWL radio, Mayor Ray Nagin (search) said that authorities were going to try to persuade people to leave. Officers will no longer be handing out water to people who will not evacuate, the mayor said.

Riley estimated that fewer than 10,000 people were left in the city. He said some simply did not want to leave their homes — while others were hanging back to engage in criminal activities, such as looting.

"We don't know how long this is going to last," he said.

Riley also said police were asking people not to return to the city for now. New Orleans is still without utilities and has collapsed power lines all over the city, Riley said.

Riley said that after nearly a week of most police efforts being aimed at rescue, the department, aided by the National Guard, was turning toward "more of a law enforcement mode now."

"We are targeting looters, we are targeting those who want to create mayhem in this city," Riley said.

However, the department is short-staffed: between 400 and 500 officers on the 1,600-member police force are unaccounted for, Riley said. Some lost their homes and some are looking for their families, Riley said.

"Some simply left because they said they could not deal with the catastrophe," Riley said.

Riley said police communications, especially with other agencies, is improving after a chaotic start.

"We have moved from chaos to organized chaos and now we are better organized," Riley said.

With thousands of active military, National Guard units and federal agencies continuing to patrol the city, "we feel that the city is very secure," Riley said.

At a news conference in Baton Rouge, Maj. Gen. Bennett Landreneau, head of the Louisiana National Guard, said he expected to have 21,000 soliders in 13 hurricane-affected parishes by the end of Monday.