MANILA (REUTERS) - Mr Ferdinand Marcos Jr has maintained his wide lead in the Philippines presidential election race in a new survey released on Monday (May 2), but some political observers say the game may not be over for closest rival Leni Robredo.

Support for Mr Marcos, the son and namesake of the ousted dictator who ruled the Philippines for two decades, remained at 56 per cent ahead of next week's ballot, while Ms Robredo, the incumbent vice-president, slipped to 23 per cent from 24 per cent a month ago in the Pulse Asia surveys.

World boxing champion Manny Pacquiao and Manila Mayor Francisco Domagoso had 7 per cent and 4 per cent support respectively. The election takes place on May 9.

The Pulse Asia survey of 2,400 people was conducted between April 16 to 21, which political analyst Temario Rivera said may not have registered the late flurry of support for Ms Robredo, who has drawn crowds of tens of thousands of people in rallies in recent days.

"We might be looking at a situation when surveys cannot fully capture what is actually happening on the ground," Mr Rivera said.

That includes a series of endorsements or late switches of allegiance in favour of Ms Robredo, 57, from mayors, candidates, governors and politicians in the past few weeks, he said.

Mr Marcos, 64, has said he would not let his strong showing in polls distract him from work needed to be done to ensure victory.

The poll released on Monday showed his running mate, Ms Sara Duterte-Carpio, daughter of incumbent leader Rodrigo Duterte, still the favourite to become vice-president, a post elected separately to the president.

Mr Duterte, whose six-year term ends late next month, has not endorsed a presidential candidate, but his political party is backing Marcos.

More than 67 million Filipinos have registered to vote in the elections, which historically have a high turnout.