Both vortex liquid and solid states of high-temperature superconductor Bi 2Sr 2CaCu 2O 8+ δ have been studied by means of Josephson plasma resonance (JPR). It is found that although the JPR frequency changes at the first-order vortex lattice melting transition (VLMT), T M, by 20–30% at low temperatures, it crosses T M almost continuously at high temperatures near T c. Such a nearly continuous change from liquid to solid state strongly implies that the phase transition is so weak that the disappearance of the superconducting phase correlations is nearly continuous. This situation may be realized by considering the strong 2D superconducting fluctuations, resulting in the strong softening of the proper plasma mode in the solid phase.