New York's $406bn (€300bn) TIAA-CREF retirement system, which provides pensions to professors, doctors and scientists in the US, has stopped building its exposure to emerging market debt because an influx of investors has soaked up available opportunities.

The news follows a report this month from Standard & Poor's Ratings Services that its upgrades of government issuers of debt in emerging market countries has soared to the highest level in 10 years.