MANILA (AFP) - Philippines authorities on Wednesday demanded that boxing great Manny Pacquiao pay a US$50 million (S$62.7 million) tax bill or risk having his assets seized, but the national hero vowed to take the fight to court.

The battle between one of the best boxers in history and the taxman has shocked his army of fans in the Philippines, emerging just days after a comeback win in the ring was hailed as a moment of hope amid the aftermath of a deadly typhoon.

Pacquiao disclosed on Tuesday that the Bureau of Internal Revenue wanted 2.2 billion pesos (S$28.6 million) for alleged unpaid taxes in 2008 and 2009, when he was at the peak of his career and one of the world's highest-earning athletes.

Pacquiao, 34, insisted he had paid his taxes in the United States, and so did not need to do so in the Philippines because the two countries have an agreement allowing their citizens to avoid double taxation.