Some 1,100 people across Africa have died from mpox, the African Union's health agency said Thursday, warning that the epidemic was "going out of control" without further action.

In all, 42,000 cases have been recorded in Africa since January, the Centres for Disease Control and Prevention (Africa CDC) said, with cases reported for the first time in Zambia and Zimbabwe.

This brings to 18 the number of African countries where mpox has been officially detected this year, it said.

"Mpox is going out of control if we don't act," Africa CDC head Jean Kaseya told an online media briefing.

"I'm so sad to say we now have more than 1,000 deaths due to mpox, as you can see this week, week 40, we have 1,100 deaths reported in total."

The majority of deaths have been in the Democratic Republic of Congo, the epicentre of the outbreak, which launched a vaccination drive earlier this month.

But Kaseya said that across the continent there were still "more new cases week after week".

"Eighteen countries is too much, we cannot continue like that," he said.

Kaseya once again urged international partners to step up and called for them to immediately release funds pledged to combat mpox.

"We want now to see concrete action on the ground to stop this outbreak," he said.

Mpox, previously known as monkeypox, is caused by a virus transmitted to humans by infected animals but can also be passed from human to human through close physical contact.

It causes fever, muscular aches and large boil-like skin lesions, and can be deadly.