How do you open the blue chests?

I am only 3-4 hours in and have so far come across a few blue chest which are locked with no obvious means to open them.

I beleive I have only seen these on the overworld so far, but there may be some in the dungeons too.

How do you unlock these blue chests?

Opening blue chests requires the "spring lock" spell. This spell is obtainable (researchable), and not a bad idea to obtain as soon as possible to avoid backtracking to open these chests.

Specifics on the requirements to obtain the Spring Lock spell (minor story/gameplay mechanic spoiler):

In Evermore, upgrade the kingdom to level 2. Build the Evermore Spellworks, and upgrade that to level 3. Finally, research the spell development for the spring lock spell at the Spellworks. Source: https://www.primagames.com/games/ni-no-kuni-ii-revenant-kingdom/tips/how-open-blue-chests-ni-no-kuni-2-unlock