Men Like Gods by H.G. Wells

Mr. Barnstaple was taken past some sleeping loggias where Utopians were lying in beds, while others who wore gas-masks waited upon them. He found that all the Earthlings and all their possessions, except their cars, were assembled in the hall of the first day's Conference. He was told that the whole party were to be removed to a new place where they could be isolated and treated.

The only Utopians with the party were two who wore gas-masks and lounged in the open portico in attitudes disagreeably suggestive of sentries or custodians.