Negotiators from the European Parliament, the European Commission and member state governments will resume talks on Thursday, the Portuguese EU presidency said.

The digital certificate could open up more EU countries to travel within the bloc as soon as late June, even as the coronavirus pandemic continues and concern about virus variants remains high.

The 'passport' would indicate whether a person has tested negative for COVID-19, has recently recovered from the virus or has been vaccinated.

This could provide the basis for waiving quarantine requirements currently in place for many trips within the bloc.

However, it remains up to each of the 27 member states to decide what kind of perks the certificate would bring within its borders.

German MEP Cornelia Ernst said the negotiators failed to agree on the core issues.

Discussions still revolved around key points such as the EU Parliament's demand for access to free tests for everyone, Ernst said after the day's negotiations.

The politicians also refused to allow individual EU countries to be given the opportunity to impose their own entry restrictions on arrivals from other EU nations.

The EU executive branch set out its proposal for a 'digital green certificate' in March, kicking off negotiations.

Justice Commissioner Didier Reynders has previously stressed that the issue of free testing is up to national governments.

Greece has already relaxed entry requirements for foreign visitors who have been jabbed, and Spain allows EU tourists in on condition of a negative test.

One sixth of the European Union's adult population is now fully vaccinated, according to the European Centre for Disease Prevention and Control.

The commission's target is to raise this to 70 per cent by September.

Australian Associated Press