English rock act Florence and the Machine will headline two US summer music festivals, which announced lineups months before expected amid growing competition.

Florence and the Machine, led by the theatrical yet introspective singer Florence Welch, will play the May 20-22 Hangout festival on Alabama's Gulf coast and the June 16-19 Firefly Music Festival in Delaware.

Firefly, which was created in 2012 to give a major festival to the densely populated US East Coast, announced a comprehensive lineup Wednesday that also included English folk rockers Mumford and Sons, the hard-edged Kings of Leon and leading house music DJ Deadmau5.

The Hangout festival, announcing its lineup on Tuesday, will also feature R&B sensation The Weeknd, star DJ Calvin Harris and veteran rocker Lenny Kravitz.

The festivals announced lineups months before previous years amid a proliferation in the United States of music festivals, which have become the key money-makers for the music industry but have put pressure on promoters to book prominent acts.

Coachella, arguably the most prominent festival which takes place in April in the California desert, generally starts the announcement season in January.

Next year is expected to see even more festivals. In New York City alone, promoters are seeking to create two more major music events in addition to Governors Ball which launched in 2011.

Florence and the Machine earlier this year won wide praise for a headlining set at England's celebrated Glastonbury festival, where the band stepped in for Foo Fighters whose frontman Dave Grohl broke his leg.

Besides Florence and the Machine, another leading British singer, Ellie Goulding, will play both the Hangout and Firefly festivals.