Nearly three months into the outbreak, new cases are doubling in some hot spots, Tedros Adhanom Ghebreyesus said in a post on X after meeting with officials in the capital, Kinshasa.
It was the second visit by the WHO director-general to the Central African country since the outbreak was declared in mid-May.
"We all agree that we must urgently and massively scale up all our efforts across all pillars of the response and by all partners," Tedros said on Wednesday.
The outbreak has accounted for 3874 confirmed cases, including 1751 deaths, as of Monday, according to the latest data from the Democratic Republic of the Congo's health ministry.
In Ituri province, the epicentre of the outbreak, families said many frontline workers had gone on strike, worsening access to health care that was already challenged by rebel conflict in one of Congo's most remote and vulnerable areas, its east near the borders of South Sudan, Uganda and Rwanda.
While some workers say they have started receiving payment in the last week for work done since the outbreak began, they are demanding improved wages.
The US Department of State said it would provide an additional $US242 million ($A343 million) in funding for immediate Ebola response and preparedness efforts in the region and for humanitarian assistance related to the outbreak.
Such funding, it said, had now exceeded $US512 million in direct assistance.
The outbreak has eclipsed all previous Ebola outbreaks in its speed of transmission and is the second-largest outbreak on record, behind the 2014-2016 West Africa outbreak that recorded more than 28,000 cases, including over 11,000 deaths.
The Bundibugyo virus that is causing this outbreak has no approved treatment or vaccine, and local officials believe it began in a remote area long before it was declared on May 15.
The outbreak is still "spreading at an alarming and unprecedented rate", the medical charity Doctors Without Borders said on Wednesday, adding: "The response is expanding but is still not reaching communities quickly enough to break transmission chains."
Dr Jean Kaseya, head of the Africa Centers for Disease and Control, said on Tuesday during a visit to Bunia that contact tracing was not working, with at least 60-70 per cent of new cases coming outside of those being monitored after exposure to patients.
