The sight of a tired-looking top White House domestic policy adviser in a Hiroshima hotel said it all: President Joe Biden may be on the other side of the world but his political fight back home over the debt ceiling has followed him.

Bruce Reed, spotted in a tracksuit having a late breakfast at the luxury hotel where Biden was staying during the G7 summit, is the White House deputy chief of staff with a focus on issues inside the United States.

Instead, for the last two days he has trailed the 80-year-old Democratic president around this southern Japanese city, "updating Potus on the status of the talks", as a senior official put it.

Those "talks" – the White House demanding that the annual extension of the government's borrowing authority proceed in order to avoid a US default and Republicans demanding Democrats first agree to slash spending – were something everyone at the G7 wanted updates on.

"It is definitely a subject of interest here at the G7," National Security Advisor Jake Sullivan told reporters on Saturday, exuding his customary intense calm.

Sullivan insisted that the debt talks had not been "generating alarm or a kind of vibration in the room" at the summit.

And Press Secretary Karine Jean-Pierre insisted that it's not a "hair-on-fire type of situation".

Yet those reassurances belie the White House's own apocalyptic warnings.

"Republicans are taking the economy hostage and pushing us to the brink of default, which could cost millions of jobs and tip the country into recession after two years of steady job and wage growth," Biden communications director Ben LaBolt said on Saturday. (AFP)