MANILA - Authorities are on the lookout for left-leaning groups that have tried to cause trouble for the 6-month closure of Boracay island, police said Tuesday.

Some progressive activists had urged workers and local officials to oppose the holiday island's closure, which will give way to the construction of sewage treatment facilities and the demolition of illegal structures, said Chief Supt. Cesar Hawthorne Binag, head of the Western Visayas police.

"Pumasok po dito iyung mga kaliwa. Pati po iyung government, kinausap nila na makipag-alliance sa kanila," Binag told radio DZMM.

"May mga dati na naghihikayat po doon sa workers na mag-aklas. Ayaw po nating maging bayolente ang sitwasyon," he added.

(Leftist groups went here. They urged the government to form an alliance with them. Some also urged workers to rebel. We do not want the situation to get violent.)

Workers and local officials have committed to cooperate with Boracay's shutdown, he said.

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A 630-strong police force, including a 138-member "crowd dispersal unit", was nonetheless deployed to Boracay, authorities had said.

They will be supported by soldiers, the coast guard, firefighters, the local peacekeeping force and some 2,000 security guards hired by private resorts.

"Sa security cluster po ay handang-handa na tayo," Binag said.

(We are fully prepared in the security cluster.)

• PNP all set for 6-month Boracay closure

Entry to the island will be limited to residents, who will be obliged to carry new identification cards and will be banned from boating and night swimming.

• Boracay residents, workers rush to get identification papers

Businesses in the area, which previously lobbied for a phased rehabilitation, have warned that an abrupt shutdown could lead to bankruptcies and job losses for many of the island's 17,000 hotel, restaurant and other tourism workers, plus some 11,000 construction workers.

The island drew 2 million visitors last year, according to official data.

The abrupt decision to close Boracay has forced hundreds of hotels, restaurants, tour operators and other businesses to cancel bookings.

• Boracay shutdown: 36,000 jobs, P56 billion revenues may be lost

The Duterte government maintains it is legal for it to deploy police and bar tourists from the island. With a report from Agence France-Presse