LIMITED POWER OF ATTORNEY
                                      FOR
                         John Hancock GA Mortgage Trust

                             SECTION 16(a) FILINGS

As an officer, trustee or shareholder of John Hancock GA Mortgage Trust (the
"Fund"), the undersigned hereby constitutes and appoints with full power of
substitution each of Ariel Ayanna, Anjali Chitre, Edward Macdonald and David
Pemstein, acting singly, the undersigned's true and lawful attorney-in-fact
to:

      (1)  Prepare and execute for the undersigned, Forms 3, 4, and 5 and
amendments thereto regarding shares of the Fund in accordance with Section
16(a) of the Securities Exchange Act of 1934 and the rules thereunder;

      (2)  File any such Form 3, 4, or 5 or amendments thereto with the United
States Securities and Exchange Commission (the "SEC") and any stock exchange
or similar authority; and

      (3)  Take any other action which, in the opinion of such
attorney-in-fact, may be necessary or desirable in connection with the
foregoing.

The undersigned acknowledges that neither the foregoing attorneys-in-fact nor
the Fund are assuming the undersigned's responsibilities to comply with
Section 16 of the Securities Exchange Act of 1934 and the rules thereunder.

This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms 3, 4, and 5, unless earlier
revoked by the undersigned in a signed writing delivered to the foregoing
attorneys-in-fact.  This Power of Attorney may be filed with the SEC as may be
necessary or appropriate.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be
executed as of this 17th day of January 2019.

                                               /s/ William T. Shields
                                               --------------------------------
                                               William T. Shields