Context : Mechanisms involved in the star formation process and in particular the duration of the different phases of the cloud contraction are not yet fully understood .
Photometric data alone suggest that objects coexist in the young cluster NGC 6530 with ages from \sim 1 Myr up to 10 Myrs .

Aims : We want to derive accurate stellar parameters and , in particular , stellar ages to be able to constrain a possible age spread in the star-forming region NGC6530 .

Methods : We used low-resolution spectra taken with VIMOS @ VLT and literature spectra of standard stars to derive spectral types of a subsample of 94 candidate members of this cluster .

Results : We assign spectral types to 86 of the 88 confirmed cluster members and derive individual reddenings .
Our data are better fitted by the anomalous reddening law with R _ { V } =5 .
We confirm the presence of strong differential reddening in this region .
We derive fundamental stellar parameters , such as effective temperatures , photospheric colors , luminosities , masses , and ages for 78 members , while for the remaining 8 YSOs we can not determine the interstellar absorption , since they are likely accretors , and their V-I colors are bluer than their intrinsic colors .

Conclusions : The cluster members studied in this work have masses between 0.4 and 4 M _ { \odot } and ages between 1-2 Myrs and 6-7 Myrs .
We find that the SE region is the most recent site of star formation , while the older YSOs are loosely clustered in the N and W regions .
The presence of two distint generations of YSOs with different spatial distribution allows us to conclude that in this region there is an age spread of ~ { } 6-7 Myrs .
This is consistent with the scenario of sequential star formation suggested in literature .