President Rodrigo Duterte has signed a law making education at all state universities free, a palace official said Friday, despite warnings from his economic advisors that the Philippines cannot afford it.

Duterte, who is known for his populist leanings, believes the long-term benefits of the measure outweigh the short-term budgetary challenges, said deputy presidential executive secretary Menardo Guevarra.

"Free tertiary education in state universities and colleges is a very strong pillar or cornerstone of the president's social development policy," he told reporters.

The bill, signed late Thursday, will spare all students at government-run colleges and universities from paying tuition and other fees, he added.

Economic officials had warned Duterte not to approve the measure, which they argue will cost 100 billion pesos (some $2 billion) a year and will mainly benefit wealthier students because only 12 percent of students in state universities and colleges belong to low-income families.

Guevarra said that now the measure had been signed, everyone needed to work together to solve the key problem facing the new bill: funding.

"Everyone including the economic managers will have to focus their attention on this particular aspect: funding for this program," he added.

Congressman Salvador Belaro, one of the authors of the bill for free state college tuition, warned it could cost some 500 billion pesos to fund the program through to 2022.

Senator Franklin Drilon has said the measure would only require 20-25 billion pesos a year, much less than the economic managers' estimate.

The Philippines has 114 state universities and colleges. Under Duterte's proposed budget for 2018, these institutions have a total allocation of 64.6 billion pesos.

This is out of a total education budget of 691.1 billion pesos, budget department documents showed.

The Duterte administration has planned a whopping $180 billion infrastructure spending until the end of the president's term in 2022. To fund that, the government has asked lawmakers to pass new revenue measures.

Duterte's economic program focuses on infrastructure spending and fiscal efficiency to lift growth to as much as 8 percent before his six-year term ends in 2022.