The explosions were likely to have come from the fuel tank of the ferry, which was carrying 129 passengers on board, most of them tourists.
The boat had completed about one-third of its journey to the resort island of Bali from Senggigi in Lombok when the explosion took place yesterday afternoon.
Among those injured were passengers from Australia, France, Italy, US, UK and New Zealand.
"No one has serious injuries. Most of the 25 patients suffered minor injuries from the impact," an official at West Nusa Tenggara hospital, Oxy Cahyo Wahyuni, said.
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"We suspected that the explosion came from the fuel tank," Anwar said.
The local police is investigating to find the cause of the incident, he added.
A member of staff at Wahana Gili Ocean, the company running the ferry operation, described the situation of the boat.
"The passengers area was a mess, with seats overturned and scattered everywhere," Ismail, who only gave his first name, told AFP.
A spokesperson for Australia's Department of Foreign Affairs and Trade confirmed that four Australians were hospitalised and that all have been released from hospital.