Non-bank financial intermediaries (NBFI) - known as shadow banks - also include insurers and now make up nearly half the world's financial assets, raising concerns among central banks about threats to overall financial stability.

Non-banks are regulated by securities regulators, who have rejected past attempts by central banks to impose bank-like rules on the sector

Global banking and securities regulators are focusing on improving the resilience of the NBFI sector to market shocks, with proposals for open-ended funds expected in coming weeks after money market funds were addressed.

"While the focus of the Committee is on the global banking system, the growth in NBFI is of importance, given the interconnections between banks and NBFIs," Pablo Hernández de Cos, chair of the global Basel Committee, which writes bank capital rules that are applied across the world.

It should be an open question whether more needs to be done to shield banks from non-bank risk, such as through macroprudential policy, which typically refers to measures such as a sector-wide capital buffer to cover a specific risk.

"We also plan to develop additional guidance with regard to NBFI risk management over the course of this year," de Cos, who is also Bank of Spain governor, said in a speech.

"While great progress has been made in shoring up banks' resilience with regard to NBFI entities, the question is whether that is sufficient?"

To date, virtually every episode of NBFI distress has involved banks, either as a direct counterpart or through indirect channels, de Cos added.

(Reporting by Huw Jones, Editing by Louise Heavens)

By Huw Jones