Single-shot nanosecond laser ablation of stainless steel and copper surfaces in ambient air and liquid water environment was studied by contact broadband ultrasonics in the important laser intensity range of 6-450 GW/cm(2), covering both regimes of surface phase explosion and formation of sub-critical ablative plasma via optical breakdown in the corresponding dense ablative plume. Similar dependences of ablative plasma pressure were obtained for the dry and wet ablation conditions, differing in their ultrasonic pulse amplitudes by the factor similar to 5 and in their pulsewidths by the factor of 1.3 (copper) and 1.6 (steel) for the wet ablation because of the dynamic water-confinement effect. Excepting the confinement effect, these results indicate the similar conditions for pressure generation via sub-critical plasma formation both for the air and water environments, enlightening promising applications of laser ablation for liquid-assisted laser peening and generation of nanoparticles in liquids. (C) 2018 Elsevier Ltd. All rights reserved.