  We present a theoretical study of an escape rate for switching from the
superconducting state to a resistive one in series arrays of strongly
interacting Josephson junctions. At low temperatures such a switching is
determined by macroscopic quantum tunneling (MQT) of a spatially extended
Josephson phase. An increase of the crossover temperature from the thermal to
quantum regimes, and a giant enhancement of MQT escape rate is obtained. Such
an effect is explained by excitation of collective charge oscillations forming
a {\it charge instanton}. Using a model of screened Coulomb interaction we
found that our analysis is in a good accord with recently published
experimental results on an enhancement of the MQT in single crystals of
high-$T_c$ superconductors.
