The fight to host major EU agencies leaving London after Brexit reaches a milestone Saturday as Brussels gives its assessment of bids, with one regulator warning the wrong choice could see a mass exodus of staff.

The European Commission, the bloc's executive arm, will publish its views on the 19 candidates to be the new home of the European Medicines Agency (EMA), and the eight bidding for the European Banking Authority (EBA).

The final decision will however not be made until November when EU states hold a secret ballot.

"It is going to be an objective assessment" based on criteria agreed on by the remaining 27 countries, European Commission spokesman Alexander Winterstein told reporters Friday.

The European Commission's assessments are not binding, although EU leaders are expected to take its findings into account, and the decision on what is a very closely-fought race will ultimately be a deeply political one.

Between them, the agencies employ more than 1,000 people and promise to bring both money and prestige to the new host cities, and the contest has sparked an intense lobbying campaign.

The cities seen as leading the race for the EMA are Amsterdam, Barcelona and Lille in France, with Athens, Bonn, Bratislava, Brussels, Bucharest, Copenhagen, Dublin, Helsinki, Milan, Porto, Sofia, Stockholm, Malta, Vienna, Warsaw and Zagreb also in contention.

The agency, which employs 900 pharmaceutical experts, biologists and doctors from every corner of Europe, evaluates medicines throughout the bloc. 

- 'Public health at stake' -

Earlier this week, the EMA warned that nothing less than "the future of public health in Europe" was at stake as it published a survey showing anywhere between 19 and 94 percent of staff planned to quit after the agency left London.

The EMA did not name the cities in question but said that for some, staff retention rates could be "significantly less" than 30 percent.

"This would mean that the Agency is no longer able to function and, as there is no backup, this would have important consequences for public health in the EU," the EMA said.

Even the best-case scenario would see one in five staff leave as a result of the move, the EMA said.

And as for the EBA, the German financial hub of Frankfurt is the frontrunner followed by Paris, Luxembourg and Prague, while Brussels, Dublin, Vienna and Warsaw are also in the running. 

The EBA, with 159 staff, is perhaps best known for its regular stress tests on the EU's financial sector in the wake of the global financial crisis.

Six countries -- Austria, Belgium, France, Germany, Ireland and Poland -- have made bids for both agencies. 

Hungary, Cyprus, Slovenia and the three Baltic states of Lithuania, Latvia and Estonia have not bid for any.

Britain will no longer be able to host the agencies as it is set to leave the EU in March 2019.

The commission is assessing the bids against six criteria agreed by the 27 remaining member states. 

These include accessibility, geographical spread, availability of schools and jobs for staff families and guarantees the agency will be able to start work as soon as Britain leaves the EU.