  Hamiltonian description of gravitational field contained in a spacetime
region with boundary $S$ being a null-like hypersurface (a wave front) is
discussed. Complete generating formula for the Hamiltonian dynamics (with no
surface integrals neglected) is presented. A quasi-local proof of the 1-st law
of black holes thermodynamics is obtained as a consequence, in case when $S$ is
a non-expanding horizon. The 0-th law and Penrose inequalities are discussed
from this point of view.
