The World Health Organisation has convened an emergency committee to discuss the threat of the case in Goma, which has fuelled fears of a breakout.
Head of the WHO, Tedros Adhanom Ghebreyesus, said: “Goma is a city of 2 million people, near the border with Rwanda and is a gateway to the region and the world.
“We cannot be too careful.”
Authorities are trying to trace anyone who came into contact with a 46-year-old pastor found to have the disease before and during a bus journey to Goma, eastern DR Congo’s largest city.
The preacher, travelling from Butembo, around 190 miles (306km) away, passed through three health checkpoints, aimed at stopping anyone sick with Ebola, but it was only spotted once he arrived in the city.
DR Congo’s health ministry said he had been quickly transported to an Ebola treatment centre after falling ill on Tuesday.
While in Butembo, the pastor held regular services in seven churches, during which he laid his hands on worshippers, including people who were ill, the health ministry said.
Dr Harouna Djingarey, infectious disease program manager for the WHO’s regional office in eastern DR Congo, said: “It’s the door of this region to the rest of the world.
“From here you can fly to go to everywhere in the world. If we don’t have the control over the contacts, some high risk contacts may fly, take a plane and go somewhere,” he added.
It is thought the disease is responsible for killing nearly 1,700 people in the country since August.
The latest official statistics list a total of 2,489 cases, of which 2,395 are confirmed. Twelve new cases were confirmed over the weekend and there were 10 deaths.
It has already spread to neighbouring Uganda.
About 700 people have recovered from infections.
More than 11,000 people died as the disease took hold across the West African region between 2013 – when the outbreak was thought to have started in Guinea – and 2016, with a handful of cases treated in the UK.
