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A multiparticle diffusion process is simulated in strip geometry. The pointlike particles are generated in a zone at constant concentration and allowed to diffuse in a semi-infinite medium with periodic boundaries. The average particle position, its concentration trend and the particle ensemble width are investigated at short and long times. Systematic deviations are observed with respect to the Fickian behaviour at the beginning of the diffusion process where a transient superdiffusive trend appears, despite the absence of particles interactions. Besides, the classical continuum approach shows a persistent lack of fit as far as the concentration at the diffusion front is concerned. The results are related with previous studies concerning collective on-lattice diffusion in a concentration gradient.