BANGKOK — For months, many Southeast Asian countries played down the threat posed by the new coronavirus. Some officials said that prayer would keep the disease away. Others expressed optimism that the tropical heat would slow the spread of the virus.

Life continued as usual. Malaysia allowed large religious gatherings. Thailand kept open its hugely popular Muay Thai boxing stadiums. In countries with struggling health care systems, like Indonesia and Myanmar, testing for infections was minimal.

Now, with the belated realization that the virus is encircling the globe in its relentless spread, countries across Southeast Asia have begun to impose strict measures, including lockdowns in the Philippines and Malaysia and the widespread closure of schools, businesses and entertainment venues in Thailand. The delays are proving dangerous, as some nations face a worrisome rise in cases without a health care system that can deal with a major outbreak.

The Indonesian president, Joko Widodo, has admitted that he misled the public about the dangers of the disease caused by the coronavirus, Covid-19, to prevent people from panicking.