Amid concerns from small businesses and central bankers about small companies' access to finance, NAB says it will start putting a greater emphasis on the strength of a business, rather than the security provided, when assessing some small business loans.

The move comes as a senior Reserve Bank official highlighted the relatively high cost of debt for smaller firms, saying competition was not as fierce as it could be in a part of the financial system that is dominated by the big four banks.

On Thursday, NAB is doubling to $100,000 the maximum amount it will extend to small firms through its online platform, which it says delivers cash within 24 hours, based largely on an automated assessment of the applicant's financial position.

A key gripe of some smaller businesses is the difficulty of accessing competitively-priced finance without providing security - which is generally a property.

"We know fast and easy access to funds is critical for small businesses as they grow. And there is often a perception that access to credit is difficult without a property or other major asset to secure against," said executive general manager business direct and small business, Leigh O'Neill.

"So we're responding by placing more emphasis on the strength of the business rather than traditional physical bricks and mortar, and we're doing this at a fair and competitive price."

NAB's online lending product, QuickBiz, allows small business customers to provide details on their finances through accounting software, and the bank says it makes decisions on applications in less than 10 minutes. The interest rate charged, at 13.85 per cent, is higher than the rates charged on low-rate credit cards.

Ms O'Neill argued the pricing was "very competitive" for this part of the market, and reflected the fact these loans were unsecured, and the product did not have other hidden costs.

Even so, small business finance has repeatedly been raised as a concern of the Reserve Bank, and a speech by the assistant governor for financial markets, Christopher Kent, highlighted the importance of funding this sector.

Small businesses employed almost half of all workers in the country outside the finance sector, but Dr Kent said competition between banks had been "less vigorous" in this part of the market, compared with the rivalry between banks in lending to larger companies.

"Lending to small businesses is dominated by the major banks and, there is less competition in this market," Dr Kent said.

"Interest rates paid by small businesses are also much higher than those paid by large businesses; it's not clear the extent to which this difference reflects the greater risk involved in extending loans to small businesses."