Covid-19 is highly likely to kill more than two million people without relentless global action to combat the disease, the World Health Organization has warned.

It comes as the United States crossed seven million confirmed coronavirus cases, according to a running tally by Johns Hopkins University.

It also said 203,240 people have died from Covid-19 in the US, which is a global high.

The novel coronavirus has killed at least 984,000 people since the outbreak emerged in China last December, according to a tally from official sources compiled by AFP.

The WHO said today that the prospect of another million deaths was not unimaginable if countries and individuals do not come together to tackle the crisis.

"One million is a terrible number and we need to reflect on that before we start considering a second million," the WHO's emergencies director Michael Ryan told a virtual news conference.

He was replying to a question by AFP, who asked if it was unthinkable that two million people could die in the pandemic before a vaccine comes around.

But Mr Ryan added: "Are we prepared collectively to do what it takes to avoid that number?

"If we don't take those actions ... yes, we will be looking at that number - and sadly much higher.

"Unless we do it all, the numbers you speak about are not only imaginable but unfortunately, and sadly, very likely."

Mr Ryan reflected on the challenges ahead in funding, producing and distributing any eventual vaccines against Covid-19.

"If we look at losing a million people in nine months and then we just look at the realities of getting a vaccine out there in the next nine months, it's a big task for everyone involved," he said.

Bruce Aylward, who heads the ACT-Accelerator - the WHO-led global collaboration to hunt for a vaccine and treatments - said people would "unnecessarily and unacceptably die" if countries and individuals sit on their hands until a vaccine comes around.

"We should not be waiting," he said.

Two million deaths "should be unimaginable. And it should not be a function of whether or not we have a vaccine. It's a function of whether or not we, as individuals, do our part to prevent transmission of this disease."