Witnesses told local television stations that they heard at least two loud blasts around midday, just as the sermon had started at Friday prayers

Indonesian authorities said on Friday they have identified a 17-year-old boy as the suspect in an attack that shook a mosque at a high school in the capital Jakarta, injuring at least 54 people.

Witnesses told local television stations that they heard at least two loud blasts around midday, just as the sermon had started at Friday prayers, from inside and outside the mosque at SMA 72, a state high school within a navy compound in Jakarta's northern Kelapa Gading neighbourhood.

Students and others ran out in panic as grey smoke filled the mosque.

Police said they had recovered a toy submachine gun belonging to the suspect and inscribed with what appeared to be white supremacist slogans. However, they brushed away speculation that the blasts were a terror attack.

"The suspect is a 17-year-old male student" who was undergoing surgery, Deputy House Speaker Sufmi Dasco Ahmad told reporters after visiting victims at a hospital. He gave no more details.

National Police Chief Listyo Sigit said the suspect was one of two students having surgery for injuries from the blasts.

"Our personnel are currently conducting an in-depth investigation to determine the suspect's identity and the environment where he lives, including his house and others," Police Chief Sigit told a news conference at the presidential palace in Jakarta.

Police Chief Sigit said investigators are still collecting information to determine a motive, including how the suspect was able to assemble a toy submachine gun with words inscribed on it including "14 words. For Agartha," and "Brenton Tarrant: Welcome to hell".

"14 words" is generally a reference to a white supremacist slogan, while Brenton Tarrant is the perpetrator of a 2019 mass shooting at a mosque and Islamic centre in Christchurch, New Zealand, that killed 51 and injured dozens of others.

"We discovered the weapon was a toy gun with specific markings, which we are also investigating to understand the motive, including how he assembled it and carried out the attack," Mr Sigit said.

Most of the victims suffered burns and injuries from flying glass. The type of explosives used was not immediately known but the blasts came from near the mosque's loudspeaker, according to Jakarta Police Chief Asep Edi Suheri.

He warned against speculation that the incident was a terror attack before the police investigation is completed.

Police confirmed they were looking into reports in local media that the suspect was a grade 12 student who had been bullied and wanted revenge by carrying out what was intended to be a suicide attack.

"We are still investigating the possibility that bullying was a factor that motivated the suspect to carry out the attack," Jakarta Police's spokesperson Budi Hermanto told reporters late Friday.

"There are several obstacles in obtaining information from witnesses as they are also victims who need medical treatment to recover," Mr Hermanto said, adding that authorities are providing "trauma healing" for students and teachers.

He revised the number of people injured to 54 instead of 55 as police said earlier, saying most of the victims were standing close to the loudspeaker and suffered hearing loss from the blasts inside the mosque. About 33 students remain hospitalized in two hospitals for burns and wounds from blast fragments.

Mr Hermanto said the capital is safe and security is under control, and he urged people not to be anxious.

Videos circulating on social media showed dozens of students in school uniform running in panic across the school's basketball court, some covering their ears with their hands, apparently to protect themselves from the blasts.

Some of the injured were carried on stretchers to waiting cars.

Shocked relatives gathered at centers set up at Yarsi and Cempaka Putih hospitals to seek information about their loved ones. Parents told television stations their children had wounds from being hit in the head, feet and hands by sharp nails and pieces of exploding objects.

Indonesia, the world's most populous Muslim-majority country, was struck by a major militant attack in 2002 when al-Qaida staged bombings on the resort island of Bali that killed 202 people, mostly foreign tourists.

In subsequent years, there have been mostly smaller, less deadly strikes that have targeted the government, police and anti-terrorism forces, as well as those considered infidels by militant groups.

Friday's attack was not the first mosque attack. In 2011, a Muslim militant blew himself up in a mosque at a police compound in Cirebon packed with officers during Friday prayers, injuring 30 people.

In December 2022, a Muslim militant and convicted bombmaker who was released from prison the previous year blew himself up at a police station in West Java, killing an officer and wounding 11 people.

Since 2023, the Southeast Asian nation has experienced what authorities call a "zero attack phenomenon." Security experts say the government is responsible for the stable situation.

Indonesian authorities identify 17-year-old suspect after mosque attack injures 54