US President Joe Biden on Wednesday slammed "Neanderthal" decisions to drop mask-wearing mandates in Texas and Mississippi, even as Covid-19 continues to rage worldwide, with Brazil hitting record deaths.

Moves by the two US states to defy federal guidelines and ditch mask requirements reflect local frustration with restrictions when Covid-19 caseloads are declining in the United States and vaccine distribution is accelerating.

Similar unrest is widespread in Europe, where the Swiss government said a referendum would be held in June on the legality of government powers to order lockdowns.

In the Dutch town of Bovenkarspel, a suspected bomb went off at a coronavirus testing center, breaking windows but not causing any injuries. Officials called the explosion, which was still under investigation, "a cowardly act of destruction."

The Netherlands has been shaken by riots against coronavirus curfews and the torching of another testing center in January.

Biden is touting a surge in vaccine production in the United States and says that by May, there will be enough supply for everyone in the country -- although it could take months more for the whole population actually to receive the shots.

But in the White House, he told reporters that this is no time to relax. More than half a million Americans have died from the coronavirus, and the toll ticks upward daily.

The Texas and Mississippi decisions were "a big mistake," he said.

"The last thing we need is Neanderthal thinking that in the meantime, everything's fine -- take off your mask, forget it. It still matters."

Rochelle Walensky, the director of the Centers for Disease Control and Prevention (CDC), echoed the warning, saying, "Now is not the time to release all restrictions."

"The next month or two is really pivotal in terms of how this pandemic goes."

- Greece, Brazil hit hard -

Increasingly, the now year-long global pandemic is boiling down to a race between the virus's spread and governments' ability to administer an ever-growing line-up of vaccines.

While cases are dropping in some countries, Greece on Wednesday extended its lockdown to March 16 and called on additional private health resources as it clocked its highest rate of daily infections this year.

"We are at the toughest part of this pandemic," Health Minister Vassilis Kikilias told reporters.

On the other side of the world, Brazil reported a second straight day of record Covid-19 deaths, bringing the total to more than 259,000.

Brazil's biggest state, Sao Paulo, declared "code red" restrictions over the coronavirus Wednesday, ordering non-essential businesses closed for two weeks.

"We're going to face the two worst weeks since March last year," said Governor Joao Doria.

"Sao Paulo and Brazil are on the brink of a health system collapse."

Doria lashed out at his political rival, President Jair Bolsonaro, for the pandemic's latest surge in Latin America's largest country.

"This is your fault. It's because of your denialism," he said, addressing the far-right president in a press conference.

Meanwhile, the Czech Republic launched new mass testing at private companies to try and control soaring infection rates.

"The situation in our hospitals is really critical. We have to employ all reserves to save lives," Health Minister Jan Blatny told reporters.

The government is in talks to receive assistance from other European countries including Germany, Poland and Switzerland, which have all offered hospital beds.

US starts to reopen

Fewer than 10 percent of over-18-year-olds in Texas have had two vaccine doses, but Republican state governor Greg Abbott said the vaccine and better testing mean normal life can resume.

"For nearly half a year, most businesses have been open either 75 percent or 50 percent and during that time too many Texans have been sidelined from employment," he told a business forum Tuesday.

"This must end. It is now time to open Texas 100 percent," he said to cheers from his audience.

Many Texans welcomed the move, saying mask-wearing was a matter of personal choice.

But the Democratic mayor of Houston described the decision as "disheartening."

Iowa and Montana eased restrictions last month, and in Massachusetts, restaurants now have no capacity limit.

Some Democratic-led cities, such as San Francisco, are also taking steps towards a post-pandemic life by allowing indoor eating and museums to open with limited capacity.