From gigantic billboards on high-rises to portraits that flank leafy boulevards, images of King Bhumibol Adulyadej dominate the streets of Bangkok. Such is the cult of personality surrounding the world's longest-reigning monarch that some analysts have made comparisons with North Korea's fervour for its supreme commander.

After seven decades on the throne, King Bhumibol is accorded semi-divine status. Celebrations will include a morning religious ceremony presided over by 770 (seen as an auspicious figure) Buddhist monks. However, the kingdom marks his platinum jubilee amid anxiety over his health. The king received heart treatment this week and has been in hospital for much of the past decade.

The king's health is a matter of intense national concern due to unease about political stability during the succession. Most Thai people have known no other monarch. Crown Prince Vajiralongkorn, the king's 63-year-old son, is the heir apparent. He has not achieved the same level of devotion that his father enjoys.

Crowds gather whenever the king's convoy travels, and many people sport the colours of royal family members on their birthdays. The national anthem is played in public places every morning and evening and people are expected to stand at attention. Old footage of the king's visits to rural communities is shown when his anthem is played in cinemas before every film. Many national holidays revolve around the royals. The king's birthday is Father's Day and Queen Sirikit's is Mother's Day.

For some, the reverence reflects conformity in a country known for adherence to age old customs and its love of uniforms. Others point to stringent royal insult laws (lèse majesté) which prevent criticism of the king – enforced with record jail terms under the junta that seized power in 2014.

The king's jubilee comes amid a crackdown on dissent ahead of August's referendum on a constitution that critics say would extend the military's influence at the expense of populist political forces emerging to challenge the establishment. If voters reject the draft charter, a general election slated for 2017 could be delayed, prolonging tension between the military-dominated establishment and its rivals seeking a quick return to electoral politics.

Educational reforms under the junta have emphasised loyalty and love of the monarchy. King Bhumibol's image is at the centre of every classroom in schools, where education is largely by rote learning.

The monarchy has not always been held so highly in Thailand. In 1946, at the age of 18, King Bhumibol inherited a throne that had barely survived the upheaval of the end of absolute monarchy in 1932. That marked what an official biography of the king described as a nadir for the monarchy. Over the following decades, the king earned the adoration of millions through work in public health and rural development, and with the help of a formidable public relations machine that returned the monarchy to prominence in a country where politics, was, and still is, largely dominated by the military.

The military has staged 19 coups or attempted coups since the end of absolute monarchy, often evoking its loyalty to the crown and defence of the monarchy in explaining its actions.