The 29-member alliance has more than 20 exercises planned this year, and will take part in the US-led Defender 2020 drill, which will see 20,000 troops deployed from the United States to Europe.

NATO Secretary General Jens Stoltenberg said the alliance was making contingency plans in case of a significant outbreak, but for now exercises would go ahead as planned.

"We are of course monitoring and following the situation very closely because this potentially has consequences also for NATO," he said in an interview in Zagreb, where he attended a meeting of EU defence ministers.

"No cancellation of exercises, but this is something we will assess as the situation evolves. We are ready to to step up the efforts and step up the measures we are implementing," he added.

Italy -- the worst-hit country in Europe by COVID-19 with 3,000 cases and more than 100 deaths -- is currently hosting NATO's Dynamic Manta submarine warfare exercise, involving 10 allied nations.

It is also set to host a five-day electronic warfare exercise starting on Sunday.

Visitor access to NATO headquarters in Brussels has been restricted, Stoltenberg said, and military commanders have been given advice on limiting the spread of the virus.

"And of course we have plans in place for business continuity, if we, for instance, have many cases in the NATO command structure or NATO headquarters," he added.