Rodrigo Duterte, a seven-term Philippine mayor, gestures while making a point during a ceremony proclaiming him as a presidential candidate at a hotel in Manila November 30, 2015. REUTERS/Romeo Ranoco

MANILA (Reuters) - A tough-talking, seven-term mayor, who has built a reputation for fighting crime in the insurgency-plagued southern Philippines, has become favorite to succeed President Benigno Aquino in May elections, an opinion poll showed on Monday.

Rodrigo Duterte, 70, mayor of Davao City, was the top-rated contender for 38 percent of 1,200 respondents, the Social Weather Stations poll said.

Senator Grace Poe, who topped surveys in June and September, slid down to second spot with 21 percent in a tie with Vice President Jejomar Binay, who led opinion polls early this year. Poe had 26 percent support in September and Binay had 24 percent.

Poe last week was barred for running because she fails to meet the 10-year residency requirement but she is hopeful that decision will be reversed on appeal.

The elections will be closely watched by investors, who fear the political succession in one of Asia’s fastest-growing economies could derail gains made during Aquino’s rule.

Under Aquino, the Philippines has seen annual economic growth of more than six percent on average, its best five-year record in four decades. He has also battled to rein in corruption.

About 54 million Filipinos are eligible to vote to choose a president, vice president and more than 18,000 local government executives and lawmakers in the general elections, which happen every six years.

Aquino’s chosen successor, former interior minister Manuel “Mar” Roxas, was fourth in the poll, falling from 20 percent support in September to 15 percent.

Political analysts said the rise in support for Duterte could be attributed to his anti-crime crusade. As mayor, Duterte has turned around the reputation of Davao, once one of the most crime-plagued cities in the country.