Donald Trump will unleash his first volley of TV ads in battleground states on Friday, according to a campaign adviser.

Ads for the GOP nominee will air by week's end in Florida, Ohio, North Carolina and Pennsylvania, according to a report by the Wall Street Journal.

Trump's general election rival, Hillary Clinton, has spent about $57 million in ads so far, bolstered by $32 million spent by pro-Clinton super PACs. Meanwhile pro-Trump groups have only spent about $4 million for their preferred candidate.

Recent polls show Trump trailing the former secretary of state in all four battleground states where he is set to launch his ads. The Trump campaign did not return a request for comment on the report.