Multi-wall carbon nanotubes (MWCNTs) containing linear C chains have been synthesised by arc discharge in liquid nitrogen. The experimental conditions used allow one to obtain nanotubes with a very thin innermost diameter, as evidenced by the radial breathing mode (RBM) features in the Raman spectra. A correlation between the RBM and the features of the C chains is reported, which gives a direct indication of how these linear carbon chain/carbon nanotube hybrid systems form. C chains are inserted only in CNTs having the innermost diameter equal to 0.7 nm, as expected.