S&P Global Ratings has upgraded Sun Life Hong Kong's financial strength and issuer credit ratings to AA from AA-, according to a Tuesday release.

The rating agency changed its view of the company's status as a subsidiary of Sun Life Financial to core from highly strategic, as the group further zones in on Asia as a main driver of its four-pillar strategy.

The subsidiary is the group's largest operating unit in Asia, with a contribution of above 40% of the region's underlying net income.

The rating agency also expects the parent to offer strategic and financial support to the subsidiary in all circumstances.

The outlook is stable, which is equalized with that of the parent, S&P said.

Changes in the parent's ratings or the importance of the subsidiary to the group's overall strategy could prompt future rating actions.