Nigerian authorities imposed a dusk-to-dawn curfew Friday in the southern state after security forces and gang members have clashed.
The measure for Rivers State would be reviewed after one week, Police Commissioner Felix Ogbaudu told reporters. The fighting has concentrated in Port Harcourt, the oil-region's largest city, which is in Rivers State.
With no reports on further fighting Friday between security forces and supporters of a top gang leader, Soboma George, troops flooded into the hardest-hit areas - and unknown numbers of residents took advantage of the calm to flee.
Nene Ibieneye, a mother of three, said the arrival of troops sparked fears of another street battle.
Security forces mounted checkpoints around the area, said residents. One motorcycle taxi driver who normally plies routes in the area said he wouldn't enter on Friday.
"I don't want to be cut down by bullets," said James Akoro.
Gunfire broke out early Thursday between security forces and supporters of gang leader Soboma George, who was being sought by police, and the sides battled in mostly empty streets for much of that day.
Officials said they believed George, who's believed to be linked to the region's main militant movement, had died in the fighting, as he was thought to be inside a building when it caught fire and burned to the ground. But a top militant leader said he had spoken on the telephone with George after the clash. The accounts couldn't be independently verified.
The military went to find George after his forces fought six days of deadly turf battles last week with supporters of another gang leader, Ateke Tom. At least 15 people died in that fight in Port Harcourt.
Over a year and a half of stepped-up violence began as militants seeking greater oil funds stepped up their bombings and kidnappings in late 2005. But criminal gangs quickly took advantage of the decreasing security situation and the region is now mired in lawlessness.