There has been a car bomb attack near an oil refinery in Nigeria's Delta region, reports say.
Militant attacks have cut Nigeria's oil production by 20%
State officials told the AFP news agency there were no casualties when the car blew up near the port town of Warri, but several cars were damaged.
The car was parked at a truck stop used by oil tankers which service the town's refinery, a military official said.
The Mend militant group said it carried out the blast, as a warning against Chinese expansion in the region.
Earlier this week, Chinese President Hu Jintao secured four oil drilling licenses for China in return for $4bn (£2.25bn) of investment in Nigeria during a two-day visit.
The Movement for the Emancipation of the Niger Delta (Mend) group had also e-mailed journalists before the explosion announcing the attack was going to take place.
Mend said the blast was "the last warning to oil industry workers" and warned China against further involvement in the region.
"We wish to warn the Chinese government and its oil companies to steer well clear of the Niger Delta," the statement said.
"The Chinese government by investing in stolen crude places its citizens in our line of fire," it said.
The militants, who carried out a car bomb attack on 20 April in the nearby city of Port Harcourt which killed two people, are demanding more local control of the region's oil wealth.
In recent months, the group has kidnapped foreign oil workers and warned them to leave the Delta.
The upsurge of attacks on foreign oil interests has cut the country's oil production by 20%.
This has cost Nigeria millions of dollars of lost revenue and helped to drive up world oil prices.