With the virus still spreading fast in Brazil -- the country with the second-highest caseload, after the United States -- Bahia Governor Rui Costa decreed a 6:00 pm to 5:00 am curfew for the state's 19 southernmost municipalities, effective until June 9.

He also ordered the closure of all but essential businesses and services in the same zone, the state government said.

"It is necessary and urgent to impose greater restrictions, after recording extremely high [infection] rates" in the area, Costa said in announcing the measures.

"If we don't act, we could see an explosion of cases and an explosion in demand for beds in intensive care units, which we won't be able to meet."

The alternative, he said, was "a large number of deaths" in Bahia, which has registered more than 21,000 cases and 700 deaths so far.

The area affected by the decree sits at the border between the two Brazilian regions hit hardest by the novel coronavirus: the southeast and northeast.

The outbreak in Brazil started in the southeast, the country's wealthy business and industrial corridor.

That region, which includes Sao Paulo and Rio de Janeiro, remains the hardest hit, with more than 200,000 cases and nearly 15,000 deaths.

But the northeast, Brazil's poorest region, has emerged as the second-hardest hit, with nearly 195,000 cases and 10,000 deaths.

Health officials believe the outbreak in the northeast is being driven partly by poor migrant workers from the region who have returned home after losing their jobs in the southeast because of virus-related business closures and stay-at-home measures.

Brazil as a whole has now registered more than 555,000 cases and 31,000 deaths.

Experts say under-testing means the real numbers are probably much higher.

President Jair Bolsonaro is a vocal critic of stay-at-home measures, arguing they are needlessly hurting Latin America's biggest economy.

The far-right leader has urged businesses to wage "war" on such measures from state authorities.