There were no reports of violence, but the presidential palace complex was locked down, initially denying journalists' access as protesters burned Duterte's effigy with a sign "Liar King" several hundred meters outside.

A pledge to act against employers who hire workers short-term and without adequate benefits helped Duterte, a former city mayor, win the presidency in May 2016.

Shortly after assuming power, Duterte warned that any company that failed to stop hiring short-term labor risked closure.

But trade unions say the practice has persisted, particularly in shopping malls and the fast-food industry.

A leader of the left-wing Bayan (Nation) movement, Renato Reyes, said the president had done what other leaders had failed to do in 30 years - unite fragmented labor groups.

"The historic unity of the working class is the direct result of the failure of the regime to bring an end to contractualisation, a major campaign promise of the president," Reyes said in a statement.

"For two years, the executive dribbled the ball, only to pass it to Congress at the last minute."

About 8,000 police and soldiers kept watching at the march. Police estimated up to 10,000 people, waving flags and carrying banners, took part.

In central Cebu, Duterte asked Congress to pass a law amending the "outdated" Labour Code "to keep it attuned to the realities of our time".

"I remain firm in my commitment to put an end to 'ENDO' and illegal contractualisation," Duterte said, referring to the commonly used term of "end of contract" among minimum wage earners.

"A mere executive order is not enough. I cannot be a legislator. It is not allowed. But, I can only implement."

He signed an executive order prohibiting illegal contracting or sub-contracting and asked the labor department to submit a list of companies "engaged in or suspected to be engaged in labor-only contraction.

There were also protests in other key cities outside the capital as workers' groups demanded higher wages, improved working conditions, including for millions of migrant workers abroad. The Philippines is locked in a dispute with Kuwait over reports of abuse of Philippine domestic helpers there.

Last month, the labor department ordered fast-food chain Jollibee Foods Corp to regularise more than 6,000 workers by making them permanent.

REUTERS