AN international nuclear watchdog's comment on tests of the Government's contingency plan suggest Hong Kong people might be told to shelter if there is a disaster at Daya Bay. The comments from the International Atomic Energy Agency (IAEA) appear to contradict government statements that only those within 20 kilometres of the Chinese nuclear plant - covering the sparsely populated island of Ping Chau and part of Mirs Bay - will need to take any action. In the summary written following an exercise of the plan undertaken in May last year, released to the public for the first time yesterday, the observers from the International Atomic Energy Agency say: ''A decision to shelter any part of Hong Kong with the exception of Ping Chau should never be based solely on predictions. ''Decisions must be made on actual corroborated measurements, ie., location and dimensions of the plume described by aerial surveillance and/or several ground measurements that corroborate predictions.'' And last night nuclear scientist Dr Bernard Weiss, who headed the IAEA test observation team, said the comments were made because government officials in the test were planning to remove people beyond that distance. ''What we were saying was, go ahead and do the calculations but don't move people [until there is more information] . . . with people in Ping Chau unfortunately you can't wait but with the others you can wait a little longer.'' His comments appear to back those of anti-nuclear campaigner Reverend Fung Chi-wood, who said he thought the Government might ask people to remain in their homes following a release, but was not revealing such plans as it feared public concern. The Security Branch, in charge of the contingency plan, denies that there are any plans other than those it has published.