Authorities all but surrendered the streets of New Orleans to floodwaters, looting and other lawlessness Wednesday as the mayor called for a total evacuation and warned the death toll from Hurricane Katrina could reach into the thousands.

The frightening estimate came as desperation deepened in the city, with gunfire crackling sporadically and looters by the hundreds roaming the streets and ransacking tiny shops and big-box stores alike with seeming impunity.