1 Introduction

From a survey of the $J=1\rightarrow0$ transitions of CO and HCN in the central positions of 20 Seyfert galaxies, we (Curran et al. 2000) found a HCN/CO luminosity ratio of $\approx$1/6 for the "distant'' sample in which the telescope beam-width exceeds $\approx$10 kpc (galaxies with a recessional velocity of  km s^-1), i.e. a global ratio similar to that of ultra-luminous infrared galaxies (ULIRGs) and over 10 times the ratio for normal spiral galaxies. This relatively high abundance of HCN, which traces dense molecular gas, in comparison to the bulk component of the gas, as traced by the CO, suggests a significant presence of molecular hydrogen densities in excess of 10⁴ cm^-3 in the Seyfert sample. The relative luminosities of CO, HCN and the far infrared (FIR) radiation lead to the conclusion $\frac{L_{\rm FIR}}{L_{\rm CO}}~({\rm distant ~Seyferts})\mathrel{\mathchoice {\... ...\hfil\cr >\cr\sim\cr}}}}10\frac{ L_{\rm FIR}}{L_{\rm CO}}~(\rm normal ~spirals)$, from which the excess far infrared flux may arise from an active galactic nucleus in addition to the star-burst activity. Furthermore, some questions were raised about the differences in the molecular gas luminosities and distributions between the distant and the near-by samples (see Paper II). In order to resolve this issue, in this work we present maps of the near-by sources, NGCs 1068, 1365, 2273, 5033 and 6814 (in conjunction with the two other near-by Seyferts, visible from SEST; the Circinus galaxy and NGC 4945), and give the global luminosity values obtained from these, the results of which will be discussed in the forthcoming Paper II.