A second Ebola patient has died in northwestern Democratic Republic of Congo, the World Health Organisation has announced, days after a fresh outbreak of the deadly disease emerged.

Genetic testing showed an infection confirmed last week was a new "spillover event", a transmission from an infected animal, and not linked to the last outbreak, which was declared over in December, the World Health Organisation said on Monday on Twitter.

The second fatality was a female relative of the first case, a WHO spokesperson told Reuters.

The first patient began showing symptoms on April 5, but did not seek treatment for more than a week.

He was admitted to an Ebola treatment centre in Mbandaka, the capital of Congo's Equateur province, on April 21 and died later that day.

Congo has seen 13 previous outbreaks of Ebola, including one in 2018-2020 in the east that killed nearly 2300 people, the second highest toll recorded in the history of the hemorrhagic fever.