The direct observation of cavitation bubbles emerging in liquid mercury under the action of mechanical impacts and theoretical investigations on the experimental results have been made. Through a glass wall, the image of cavitation bubbles appearing near or in contact with the wall was captured by high-speed cameras. Discrepancies found between the bubbles' growth rates determined experimentally and given by a single-bubble theory have been discussed using a theoretical model of Rayleigh-Plesset type that takes into account bubble-bubble and bubble-wall interactions. A theoretical equation for the asymptotic growth rate in a multibubble case has been given and time dependence of the growth rate under a constant negative pressure has been clarified.