Spain's new king Felipe VI was sworn in today in a relatively modest ceremony which monarchists hope will usher in a new era of popularity for the troubled royal household.

He called immediately for Spain to stay united but respect the cultural differences among its regions, ending a speech by saying "thank you" in four languages: Castilian Spanish, Basque, Catalan and Galician.

Felipe became king after his father, Juan Carlos, abdicated earlier this month following a series of scandals that led many Spaniards - especially younger generations - to question the role of the monarchy itself.

One of the biggest challenges for Felipe will be whether he can use his symbolic role to spur dialogue between the leaders of Spain and the wealthy north-eastern region of Catalonia, where there is a growing independence movement.

The new king, who is 46, wore military uniform with a sash and swore loyalty to Spain's constitution before addressing dignitaries gathered in the lower house of Parliament with a long portion of his speech dedicated to the issue of national unity.

He said: "There is room for all of us in a united and diverse Spain.”

He stressed respect for the diverse cultures and languages within Spain, a clear message to people in Catalonia and Basque Country who want to break away from Spain

The multilingual gesture, however, got a cool response from the regional leaders of Catalonia and Basque Country, who were sitting in the Parliament listening to the speech and were notably restrained in their applause.

After the ceremony the king rode in an open Rolls Royce through central Madrid with his wife, Queen Letizia, a former journalist and an escort of mounted guards with tasselled helmets in a route decorated by red and yellow flowers, the colour of Spain’s flag.

Thousands of well-wishers, including tourists, lined the route, waving flags and shouting "long live the king."