June 21 (Reuters) - Organisers of the Tokyo Olympics are expected to decide on Monday to allow up to 10,000 domestic spectators at events as part of a pledge to deliver a "safe and secure" Games amid the coronavirus pandemic.

Japan's top medical adviser said last week that having no spectators at the Games would be the "least risky option."

Following are quotes from experts on the infection risks posed by having audiences at the Games:

KENJI SHIBUYA, FORMER DIRECTOR OF THE INSTITUTE OF POPULATION HEALTH AT KING'S COLLEGE LONDON

"We should consider all risk-mitigation measures based on empirical data - including testing all spectators and measures to prevent contacts, both inside and outside venues, and aerosol transmission. That should have been presented by experts long time ago, including options to cancel and postpone the Games."

"No spectators would be the least risky, but there are ways to minimise risks, for example, by testing and ventilation."

"The fundamental problem is a complete lack of open, transparent, scientific discussion and consensus-building processes, globally, on the conditions under which the Olympic Games could be held in a secure and safe manner. That is irresponsible."

TARA KIRK SELL, OLYMPIC SILVER MEDALIST, PROFESSOR AT THE JOHNS HOPKINS BLOOMBERG SCHOOL OF PUBLIC HEALTH

"If they decide to have fans, there definitely would need to be space for spectators to spread out. But it's not in the venue that I'm worried about - it's mass transit to and from there and dining out in groups in close settings around the events."

"So while I think some fans would be fine, I think that attention should be paid to the ancillary activities. It's a lot harder to organise fans than it is athletes and staff who are there to compete."

HARUKA SAKAMOTO, PHYSICIAN AND RESEARCHER AT KEIO UNIVERSITY IN TOKYO

"It would be preferable to have no audience from the standpoint of infectious disease control."

"Personally, I am concerned not just about the increase in the number of people coming to watch the Olympics itself but also about the loosening of people's sense of urgency by hosting the Olympics with spectators."

"We need to continue to take strict measures against COVID-19 for a little while. However, together with the rapid rolling out of the vaccination campaign, and now that the state of emergency has been lifted in Tokyo, it is obvious that there are many people who think it is okay to go back to their daily lives."

"It's easy to imagine that more and more people will think, 'If the Olympics can be held with spectators, it's okay for us to travel,' which may cause the increase of COVID-19 positives."

EYAL LESHEM, DIRECTOR OF THE CENTER FOR TRAVEL MEDICINE AND TROPICAL DISEASES AT SHEBA MEDICAL CENTER IN ISRAEL

"These are huge stadiums, and there's probably an orderly and safe way to put in up to 10,000 people with sufficient social distancing."

"My recommendations would be to create physical conditions that are more suitable for gathering fans to mitigate the risk. So the lines are long enough and allow for social distancing. There is enough masking and hand washing in the facilities and there is no crowding."

"You need to make sure public transportation is secure and people arrive long enough before the event to be seated."

"The other side is that enough public health capacity exists at the sites to identify local outbreaks and trace contacts and test them. So that even if there are introductions of the virus into venues, it is possible to identify these contacts and quarantine them and monitor them."

"Many of the public suffer from what we call 'pandemic fatigue.' They're tired of masking, they tend to a loosen or be lax with the recommendations, and these weeks with these mass gatherings could potentially cause an increase (in infections)."

Recent sporting events in Europe and religious festivals in Israel "tell us that mass events can be held with relative safety when there is a high level of population protection by vaccine or past infection." (Reporting by Rocky Swift in Tokyo; Editing by Lincoln Feast.)