The embryonic body axis is composed of tissues that elongate at the same pace despite exhibiting strikingly different cellular organization. Whether their co-elongation is coordinated remains unclear. Here we report evidence of mechanical coupling between axial and paraxial tissues. Combining microsurgery and live-imaging in avian embryos, we found that the presomitic mesoderm (PSM) compresses the neural tube and notochord promoting their convergence and elongation. Computational simulation predicts cell motility in the PSM to generate compression that causes axial tissues to push the caudal progenitor domain, which we tested experimentally. Surprisingly, this axial push is in turn required for the progenitor addition that sustains PSM growth. Together our results show that forces produced by collective cell dynamics couple different elongating tissues into an engine-like positive feedback loop.