The ferry carrying at least 65 people, including passengers and crew, was making a five-kilometre (3.2-mile) crossing from eastern Java island to Bali when it tilted and sank in bad weather late Wednesday, witnesses and officials said.

As of Friday morning, 30 people were still missing after 29 were plucked from the water to safety. 

Rescue officials said one of the six found dead was a three-year-old boy.

Rescuers deployed assets to carry out searches by sea and air on Friday, widening their efforts along the coastlines of eastern Java and Bali, National Search and Rescue Agency operations official Ribut Eko Suyatno told reporters. 

"The land search rescue unit... we ask to comb through the Ketapang beach from north to south. Also likewise for Gilimanuk," he said.

The ferry passage from East Java's Ketapang port to Gilimanuk port on Bali -- one of the busiest crossings in the country -- takes around one hour and is often used by people travelling between the islands with a car.

Local rescue officials said the KMP Tunu Pratama Jaya vessel sank 25 minutes into its journey.

At least 306 rescuers were deployed Friday for the search effort, the Java-based Surabaya search and rescue agency said.

The search was temporarily halted overnight and resumed around 8:00 am (0000 GMT) Friday in Bali.

The rescuers called off the search on Thursday evening due to a "visibility problem", Nanang Sigit, the head of East Java rescue agency told Reuters, adding that 29 people had been rescued on Thursday.

Rescuers had deployed inflatable boats, a larger rescue vessel and a helicopter to aid the search on Thursday, made up of dozens of personnel, including navy and police officers.

The search for the missing since Thursday morning had been hampered by strong currents and winds, the national rescue agency said. 

Video provided by national rescue agency Basarnas showed what appeared to be the body of one person being carried to shore from a fishing boat in calm seas.

At least four survivors were found early on Thursday after saving themselves by climbing into the ferry's lifeboat.

Initial search efforts were hampered by bad weather, with waves as high as 2.5 metres (8 feet) and strong winds.

The ferry's manifest showed 53 passengers and 12 crew members but it is common in the country for the actual number of passengers on a boat to differ from that document.

Marine accidents are a regular occurrence in Indonesia, in part due to lax safety standards and sometimes due to bad weather.

In March, a boat carrying 16 people capsized in rough waters off Bali, killing an Australian woman and injuring at least one other person.   

In 2018, more than 150 people drowned when a ferry sank in Toba Lake, of the world's deepest lakes.