Hundreds of thousands of Americans have enrolled to vote following Taylor Swift’s politically charged Instagram message, declaring her support for two Democratic candidates.

The American singer’s public endorsement of Tennessee Democrats Phil Bredesen and Jim Cooper sparked about 240,000 new voter registrations within a day, according to website Vote.org.

In the lengthy Instagram post which caused the spike in registrations, Swift said although she had been “reluctant” to reveal her political views, the looming November 6 midterm elections necessitated a reminder to vote.

“As much as I have in the past and would like to continue voting for women in office, I cannot support Marsha Blackburn. Her voting record in Congress appalls and terrifies me,” she warned her more than 112 million Instagram followers.

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A post shared by Taylor Swift (@taylorswift)

About 102,000 of the registrations since Sunday were among voters between 18 and 29 years old, according to the site, which helps people register online.

Although it was unable to determine the extent to which Swift’s post lead to the sudden rise in enrolments, Vote.org confirmed “a massive surge in the 18-24 and 25-29 voters”.

Vote.org recorded 57,000 new registrations in all of August and 190,000 in October.

The registration deadline is Tuesday in Tennessee and more than a dozen other states.

Wading into politics can be dicey for artists with roots – and fans – in country music, the dominant genre of red state America. The country crossover band Dixie Chicks generated a firestorm of criticism when the band publicly disavowed the US invasion of Iraq in 2003.

President Donald Trump dismissed Swift as an uninformed voter. “Let’s just say I like Taylor’s music about 25 per cent less now, OK?”, he told reporters on Monday.

Former Arkansas Governor Mike Huckabee also chimed in saying her endorsements “won’t impact the election unless we allow 13-year-old girls to vote.”

-With AAP