* Explosion causes roof to collapse, blows out wall

* At least 40 injured, 1 missing at North Carolina plant (Updates number of missing, adds company comment)

WILMINGTON, N.C., June 9 (Reuters) - An explosion caused parts of the roof to collapse on Tuesday at a ConAgra Foods Inc (CAG.N: Quote, Profile, Research) processing plant in Garner, North Carolina, injuring more than 40 people and leaving one missing, police said.

Three people had serious burns while others suffered injuries ranging from broken bones to inhalation of smoke and toxic fumes, local news media reported.

One worker was still unaccounted for but there were no reports of any deaths, said a Garner police officer, Sergeant Joe Binns.

The 500,000-square-foot plant in Garner, just south of the state capital of Raleigh, employed 900 people in three shifts and made Slim Jim meat sticks, ConAgra said.

The explosion started a fire and blew out a wall that fell onto a row of parked cars, crushing them. People at the scene reported a strong smell of ammonia fumes.

The cause of the blast was unknown. Television footage showed rescue workers in hazardous-materials suits at the plant, where the roof collapsed in several places.

ConAgra, which acquired the plant in 1998, said it was cooperating with local authorities and sending a team of experts to the facility.