Authorities say five people have been taken into custody.
Sheriff Michael Tregre said the incident started around 5:30 a.m. when a gunman opened fire for unknown reasons on a deputy working an off-duty traffic detail along a highway that connects U.S. Highway 61 with the busy industrial corridor along the Mississippi River. That deputy was wounded.
The deputy was able to radio a description of the gunmen and their car. Someone then called deputies about a speeding car matching the description of the suspects' vehicle, and officers tracked it to a nearby trailer park.
When officers found the car, they handcuffed a suspect outside a trailer, then knocked on its door. Tregre said someone with a dog answered.
"Another person exited that trailer with an assault weapon and ambushed my two officers," Tregre said.
Two deputies were killed and a third was wounded.
Two suspects were wounded in the shootout before officers subdued them, Tregre said.
The slain deputies were identified as Brandon Nielsen, 34, and Jeremy Triche, 28. The wounded officers were Jason Triche, 30, and Michael Boyington, 33. They were being treated at area hospitals, but the extent of their injuries was not known.
The suspects were not immediately identified. They are currently hospitalized.
Gov. Bobby Jindal ordered the state flags to be flown at half-staff over the state Capitol and all public buildings and institutions until sunset Friday.
ABC News and The Associated Press contributed to this report.