  We present the discovery and early observations of the nearby Type II
supernova (SN) 2024ggi in NGC 3621 at 6.64 +/- 0.3 Mpc. The SN was caught 5.8
(+1.9 -2.9) hours after its explosion by the ATLAS survey. Early-phase,
high-cadence, and multi-band photometric follow-up was performed by the Kinder
(Kilonova Finder) project, collecting over 1000 photometric data points within
a week. The combined o- and r-band light curves show a rapid rise of 3.3
magnitudes in 13.7 hours, much faster than SN 2023ixf (another recent, nearby,
and well-observed SN II). Between 13.8 and 18.8 hours after explosion SN
2024ggi became bluer, with u-g colour dropping from 0.53 to 0.15 mag. The rapid
blueward evolution indicates a wind shock breakout (SBO) scenario. No hour-long
brightening expected for the SBO from a bare stellar surface was detected
during our observations. The classification spectrum, taken 17 hours after the
SN explosion, shows flash features of high-ionization species such as Balmer
lines, He I, C III, and N III. Detailed light curve modeling reveals critical
insights into the properties of the circumstellar material (CSM). Our favoured
model has an explosion energy of 2 x 10^51 erg, a mass-loss rate of 10^-3
solar_mass/yr (with an assumed 10 km/s wind), and a confined CSM radius of 6 x
10^14 cm. The corresponding CSM mass is 0.4 solar_mass. Comparisons with SN
2023ixf highlight that SN 2024ggi has a smaller CSM density, resulting in a
faster rise and fainter UV flux. The extensive dataset and the involvement of
citizen astronomers underscore that a collaborative network is essential for
SBO searches, leading to more precise and comprehensive SN characterizations.
