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According to the current paradigm of galaxy formation, the first galaxieshave been likely formed within large dark matter haloes. The fragmentation ofthese massive haloes led to the formation of galaxy protoclusters, which areusually composed of one to a few bright objects, surrounded by numerous fainter(and less massive) galaxies. These early structures could have played a majorrole in reionising the neutral hydrogen within the first billion years of theUniverse; especially, if their number density is significant.Taking advantageof the unprecedented sensitivity reached by the \textit{James Webb SpaceTelescope (JWST)}, galaxy protoclusters can now be identified and studied inincreasing numbers beyond $z\geq\ $6. Characterising their contribution to theUV photon budget could supply new insights into the reionisation process. Weanalyse the first JWST dataset behind SMACS0723-7327 to search forprotoclusters at $z\geq6$, combining the available spectroscopic andphotometric data. We then compare our findings with semi-analytical models andsimulations. In addition to two bright galaxies ($\leq$26.5 AB in F277W),separated by $\sim$11\arcsec and spectroscopically confirmed at$z_{spec}=7.66$, we identify 6 additional galaxies with similar colors in a$\theta\sim20$\arcsec radius around these (corresponding to R$\sim60-90$ kpc inthe source plane). Using several methods, we estimate the mass of the darkmatter halo of this protocluster, $\sim$3.3$\times$10$^{11}$M$_{\odot}$accounting for magnification, consistent with various predictions. The physicalproperties of all protocluster members are also in excellent agreement withwhat has been previously found at lower redshifts: star-formation main sequenceand protocluster size. This detection adds to just a few protoclusterscurrently known in the first billion years of the universe.

A lensed protocluster candidate at $z=7.66$ identified in JWST observations of the galaxy cluster SMACS0723-7327