Indonesia's second-largest party Golkar appointed a top loyalist of President Joko Widodo as its new chief on Wednesday, a move members say could allow the outgoing president to retain political influence long after he leaves office in October.

Bahlil Lahadalia, the newly appointed energy minister and the president's right-hand man, was chosen as party leader at the annual congress of Golkar, the party of the late autocrat President Suharto, who ruled Indonesia for three decades until 1998.

The hugely popular Widodo, better known as Jokowi, has served the maximum two terms allowed and his immense political clout helped ensure former rival Prabowo Subianto won February's presidential election with a huge margin.

Four Golkar sources, several speaking on the sidelines of the congress on the condition of anonymity, told Reuters Bahlil's appointment could help Jokowi to secure his legacy after Prabowo takes power.

Golkar members have said Jokowi, who hails from the island of Java, has been quietly angling to shore up his power base through the party before stepping down. Jokowi's office did not immediately respond to a request for comment.

During his speech to the congress, Bahlil stressed the party must be unified and in an apparent reference to Jokowi, he gave a veiled warning to its members to stay in line.

"If we play around with the king of Java, it will be dangerous for us," he said.

Bahlil's appointment comes during a transition period in which Prabowo has been fast consolidating power ahead of his presidency, culminating in him securing a parliamentary majority late last week, with support from parties that had backed his election rival.

As the largest party in the parliamentary coalition, Golkar could be central to the success or failure of Prabowo's policy agenda, giving it significant bargaining power. Prabowo's Gerindra party is the second largest in the alliance.

"When Jokowi steps down as president he won't have a political tool anymore," said one senior Golkar member.

"How will he maintain the balance with the new administration? He must take over, but he can't take over Golkar alone."

"Bahlil has proven his loyalty for all these years, so Jokowi trusts Bahlil," the Golkar member added.