By Carolina Mandl

SAO PAULO, Aug 27 (Reuters) - Brazil's most prominent financial startup, Nubank, has raised $300 million in equity investments, according to a filing with the U.S. Securities and Exchange Commission.

Five investors participated in the deal, according to the document, which did not disclose their names.

News of the document, which was filed on June 19, did not surface until this week when a Brazilian financial blog noted it.

Nubank declined to comment on whether the equity capital constitutes a new funding round, but data from Crunchbase described it as a "venture round."

Existing investors in the Brazilian financial technology firm include TCV, Tencent Holdings Ltd, DST Global, Sequoia Capital, Dragoneer, Ribbit Capital, Kaszek and Thrive Capital.

Nubank, which offers credit cards - which typically carry a fee in Brazil - for free, reached 26 million clients in June. That makes it Brazil's second-largest credit card issuer, just behind the country's top lender, Itau Unibanco Holding SA , according to a note by UBS analysts.

The Brazilian firm narrowed its first-half loss to 95 million reais from a loss of 140 million reais in the same period a year earlier, as the bank added 6 million new clients.

In contrast with Itau, Banco Bradesco SA and Banco Santander Brasil SA, which were hit by the coronavirus pandemic, Nubank's credit card transactions rose 54% in the first half. It also presented a "healthy" asset quality trend, UBS added.

(Reporting by Carolina Mandl in Sao Paulo Editing by Matthew Lewis)