(Corrects timetable of delivery in second paragraph)

* Deliveries to begin 'after eight weeks starting August'

* Philippines has secured 113 mln doses from vaccine suppliers

* Government wants to vaccinate up to 70 million Filipinos

MANILA, June 20 (Reuters) - The Philippine government has signed a supply agreement for 40 million doses of the COVID-19 vaccine developed by Pfizer Inc and BioNTech SE in its biggest coronavirus vaccine deal to date.

Deliveries of the vaccine, among several brands of coronavirus shots allowed for emergency use in the Southeast Asian country, will begin in late September, Carlito Galvez, head of the government's COVID-19 vaccine procurement, said on Sunday.

The Philippines last week started a programme to vaccinate 35 million people working outside their homes, while continuing to inoculate priority sectors such as healthcare workers and elderly citizens, hoping to achieve herd immunity this year.

More than 8 million doses have been administered, of which about 6 million were for first dose, suggesting a slow vaccine rollout that puts the government's target to vaccinate up to 70 million people this year in doubt.

Vaccine supply around the capital Manila remains limited, while COVID-19 cases in several provinces have surged, complicating efforts to ramp up the immunisation drive in a country with some of Asia's largest numbers of infections and deaths.

With the latest deal, the Philippines has secured the delivery of 113 million doses from five vaccine manufacturers - also including China's Sinovac with 26 million doses, Russia's Sputnik V with 10 million doses, 20 million doses from Moderna and 17 million doses from AstraZeneca.

The ramp-up comes as Taiwan was expecting 2.5 million doses of the Moderna vaccine to arrive on Sunday from the United States, more than doubling the arsenal of the semiconductor-producing island as it deals with a rise in domestic infections.

The Philippines also expects vaccine deliveries from the international COVAX facility to reach 44 million doses, while 16 million doses of vaccines developed by Novavax and Johnson & Johnson were still under negotiation, Galvez said.

The new arrangement "will significantly boost our national immunisation programme and will enable us to realize our goal of achieving herd immunity by year-end," he said.

The Philippines will allow the Pfizer-BioNTech vaccine to be given to children aged 12 to 15, possibly starting later this year when the vaccine inventory will have increased and the inoculation of the priority sectors has been completed, he said.

(Reporting by Enrico Dela Cruz; Editing by William Mallard and Christopher Cushing)