US pharmaceutical company Johnson & Johnson has asked the European Union's drugs regulator for emergency authorization of its single-shot coronavirus vaccine.

The European Medicines Agency (EMA) said on Tuesday that it will assess the vaccine "under an accelerated timetable" and that its opinion could come by the middle of March.

The shortened timetable is possible because the EMA has already been examining data from Johnson & Johnson during a rolling review.

A rolling review allows companies to submit trial results as they become available and is quicker than a standard review process, the Amsterdam-based regulator said.

If the vaccine's safety and efficacy is determined, the Johnson & Johnson jab would be the fourth approved by the regulator and the European Commission after ones by BioNTech/Pfizer, Moderna and AstraZeneca.

The one-dose shot could provide a boost to the EU's vaccination campaign, which is under fire for its sluggish pace. The commission has ordered doses for 200 million people from Johnson & Johnson.