European Commission chief Ursula von der Leyen has warned that coronavirus emergency measures taken by EU countries must be "limited", after Hungary's nationalist leader Viktor Orban took on sweeping powers.

Brussels' top official did not single out Mr Orban or Hungary by name in her statement, but it came a day after he adopted rule by decree, claiming extraordinary powers ostensibly to combat the Covid-19 pandemic.

"The European Commission will closely monitor, in a spirit of cooperation, the application of emergency measures in all member states," she tweeted.

"We all need to work together to master this crisis. On this path, we'll uphold our European values and human rights. This is who we are and what we stand for."

Mr Orban's spokesman for international relations responded to the EU statement directly, also on Twitter, saying: "We completely agree. 

"That's why the Hungarian state of emergency and extraordinary measures are congruent with the treaties and Hungarian constitution and targeted exclusively at fighting the coronavirus," he insisted. "It upholds EU values, rule of law, press freedom."

In a separate statement read out by her spokesman, Ms von der Leyen admitted: "Over the past weeks, several EU governments took emergency measures to address the health crisis caused by the outbreak of the coronavirus.

"We are living in extraordinary times, and governments, in principle, need to have the necessary tools to act rapidly and effectively to protect the public health of our citizens," she added.

But, in a clear but unstated reference to events in Hungary, she insisted: "Any emergency measures must be limited to what is necessary and strictly proportionate. They must not last indefinitely."

"Democracy cannot work without free and independent media," she said.

Hungary is threatening prison sentences for journalists who publish what it deems "falsehoods" about the virus or the measures against it.

Critics at home and abroad have condemned Hungary's "anti-coronavirus defence law", saying it gives Mr Orban unnecessary and unlimited power and is a means of cementing his position rather than battling the virus.

After declaring a state of emergency on 11 March, the new law passed yesterday gives Mr Orban the power to indefinitely rule by decree until his government decides the emergency is over.

It removes the current requirement for MPs to approve any extensions to decrees. Elections cannot be held either during the emergency period.

The parliament, where Mr Orban's Fidesz party enjoys a dominant two-thirds majority, passed the bill by 137 votes to 53.

"At the end of the emergency, all powers will be fully restored" to parliament, said Mr Orban after the vote, dismissing opposition fears of a long-running period of rule-by-decree.

The vote marked another controversial milestone in Mr Orban's fractious decade in power. 

Since the self-styled "illiberal" nationalist won power in 2010, he has transformed Hungary's political, judicial and constitutional landscape.

The 56-year-old has frequently clashed with European institutions, NGOs and rights groups, with the EU suing Hungary for "breaching" its values - charges fiercely denied by Budapest.

Among the international bodies expressing concern over the bill before it became law were the UN human rights office, the Council of Europe, and the Organisation for Security and Co-operation in Europe.

Mr Orban has given short shrift to criticism of the coronavirus law, accusing critics of alarmism and telling "European nit-pickers" to let Hungary defend itself against COVID-19.

Justice Minister Judit Varga told foreign reporters last week that the constitutional court could provide oversight, while parliament could revoke the decrees at any time. 

The opposition were "fighting imaginary demons and not dealing with reality," she said.

A government spokesperson Zoltan Kovacs said that the decrees were also time-limited by the pandemic itself, which "hopefully ends one day". 

Last week, opposition MPs warned they did not trust Mr Orban not to abuse indefinitely granted special powers. They refused to support fast-tracking the bill without time deadlines. 

Many cited a so-called "state of crisis caused by mass migration" that Mr Orban's ruling Fidesz party declared in 2016 and which remains in place, despite migration numbers to Hungary having fallen sharply since then. 

The fiercely anti-immigration Mr Orban has blamed migration for bringing the virus to Hungary, saying "primarily foreigners brought in the disease".

The first two confirmed coronavirus cases in the EU member state of 10 million were Iranian students.

Hungary has since reported a total of 447 cases with 15 deaths. More than 13,300 tests have been carried out, the government said Monday.

"The press and non-governmental organisations now have a particularly important role to play in controlling the government," said a statement after the vote by the Hungarian Helsinki Committee refugee rights group.