At least three people including a toddler are dead after the boat they were taking to Australia sank off the coast of Java.

Indonesian authorities said 27 others were rescued after their boat broke apart off a beach near the town of Garut in West Java about 6am (10am AEDT) on Monday.

An Indonesian search and rescue agency official said most of the asylum seekers appeared to be from Bangladesh and Myanmar.

"We received information from local fishermen," the official said.

"The dead child's identity and other details are still unknown."

He said the child was believed to be about two years old.

Immigration Minister Scott Morrison earlier told parliament the government was aware of the incident but that Australian authorities were not asked for help.

However, Mr Morrison said the Australia Embassy in Jakarta had only been advised of two deaths, with several other people in critical condition.

He said the sinking again highlighted the dangers of people smuggling.

"There have been reports of three deceased persons," the minister said.

"This further loss of life is tragic and this latest incident again reflects the dangers of people smuggling, particularly in this most dangerous time of the year, and the need to be deploying all our efforts to prevent people getting on these boats."

The sinking comes amid a sharp decline in boat traffic, but also at the onset of the monsoon season, which makes conditions in waters between Indonesian and Australia much more perilous.