In baby-blue caps and yellow scout scarves, an army of royal volunteers is sprucing up Thailand before this weekend's coronation -- a projection of unity and loyalty to the unassailable crown in a divided kingdom that remains locked in political crisis.

The "Jit Arsa" programme -- or Spirit Volunteers -- has billowed out across Thailand since it was founded in 2017 by Thai King Maha Vajiralongkorn ahead of the cremation of his late father Bhumibol Adulyadej.

From planting mangroves in southern Trang to scrubbing pavements in northern Tak, or hanging miles of orchid garlands in historic Bangkok, the mass mobilisation is coming to a head with the May 4-6 coronation just days away.

The corps, now at least five million strong, has evolved as a way for many Thais to conduct acts of civic service in the new king's name.

It is also a way for a monarch who spends much of his time overseas to connect with his subjects in a kingdom where royalism leans heavily on ritual, symbols and mass demonstrations of fealty.

Bhumibol, who died in 2016 after a reign spanning seven tumultuous decades, was revered by most Thais, and his image remains omnipresent in many homes and shops.

His 66-year-old heir is not as well known by his subjects, and his three marriages and colourful private life when younger have been the subject of gossip in the past.

For the majority of Thais, Vajiralongkorn's elaborate three-day coronation will be the first they have witnessed and curiosity is mounting.

The official Spirit Volunteers song blared over loudspeakers at the Bangkok headquarters of Thai Post on a recent day dedicated to a clean-up.

"We work without hoping to gain anything," the joyful lyrics said.

Staffer Narong Denleemor, 49, said he had taken part in countless volunteer events since the passing of king Bhumibol.

"I can't explain by words -- it's all in my heart," he said of his motivation, eyes welling with tears.

Thai Post is one of many institutions -- from private companies to state offices -- corralling employees into a volunteering frenzy.

In Bangkok, the site of the first coronation since 1950, state officials have immersed themselves in preparation duties.

"This kind of event doesn't happen every day," policeman Pongpat Sumangkaset, 22, as he waited in the scorching sun near the Grand Palace during last Sunday's rehearsal.

-- 'Manufactured social unity' --

Thailand's royal family, one of the world's richest, enjoys support from Bangkok's political and business elite.

It is buttressed by an advanced palace PR machine that stamps royal imagery across the country, and shielded by a harsh lese majeste law rendering critical discussion about the king near impossible.

All media inside Thailand must self-censor and accusations of royal defamation are taken extremely seriously by the police and courts.

But the monarchy's most important ally is the powerful military, whose royally appointed generals have staged more than a dozen coups in Thailand since the end of absolutism -- the latest in 2014.

Analysts detect shades of military conformity, organisation and training in the "Jit Arsa" scheme.

The herd mentality "harks back" to the Village Scouts, said Thai specialist Paul Chambers of Naresuan University, referring to an ultra-royalist volunteer group started by the military in the 1970s.

Deployed to counter the pro-democracy student protests during that period, Village Scouts were linked to the Thammasat University massacre on October 6, 1976, in which at least 46 people were killed.

Divisions remain sharp in Thailand, a country trapped for over a decade in a spin-dryer of coups and short-lived civilian governments.

The recent March 24 poll showed a kingdom cut in two between those weary of the military injecting itself into politics -- and pro-junta supporters.

There is currently no new government, but many expect a junta-allied party to walk back in as a civilian administration.

Official results are expected May 9.

Like the Village Scouts, the Spirit Volunteers could, if needed, be marshalled into a "mob enforcer" in an attempt "to manufacture social unity", Chambers added.

Fresh from the disputed election, political parties have also been keen to show their volunteer spirit.

Straight-backed and beaming in a yellow polo in an Instagram post, Thai Raksa Chart leader Preechaphol Pongpanit, signed up to the volunteers last week "to show loyalty" to the king.

His party was disbanded shortly before the poll after nominating the king's elder sister Princess Ubolratana as a candidate for prime minister.