They clean streets, dredge up dirty canals, and sometimes direct traffic all for free, in the name of Thailand's king.

What began as a way to let the public help with the funeral of the last king has grown into a 4 million-strong civilian army.

Their blue and yellow outfits mark people who have jumped at the change to serve King Maha Vajiralongkorn.

Their good deeds are boosting his image both ahead of his coronation later this year and as he shakes up royal affairs.  

Palace officials told Reuters they fed around 4,000 people every day on top of other duties like cleaning toilets and picking up garbage.

Volunteers have to go through an initiation process.

They line up and bow in front of the king's portrait before they give it a military-style salute, which they'll do before every community activity.

This public face of King Vajiralongkor may give him a PR boost as he reshapes the monarchy.

Some experts say he's trying to distance himself from the military, which has held power since a 2014 coup.