Thousands of tourists in Rome have been kept out of the Colosseum by a union meeting, prompting the culture minister to vow measures to make sure it does not happen again.

Dario Franceschini hit out after tourists "were left to wait in line in front of the whole world, this time at the Colosseum, the most important archaeological site in Rome".

He said premier Matteo Renzi had agreed to pursue measures to protect Italy's cultural treasures from strikes, with new regulations defining Italian monuments and museums as essential services.

It was not the first time a labour dispute had left tourists waiting. A strike at Pompeii earlier this summer left lines of visitors baking in the sun outside the World Heritage archaeological site.