Police were looking to question the builders of an elevated walkway that collapsed at the Indonesia Stock Exchange yesterday, injuring 72 people.

Key points: 72 people were injured, Jakarta police confirmed

72 people were injured, Jakarta police confirmed Collapse not caused by a bomb, police official said

Collapse not caused by a bomb, police official said Mezzanine floor fell on a crowded reception area

A group of university students from the island of Sumatra, visiting the building on a study tour, were among the worst injured and were in hospital being treated for fractures and breaks.

At least 17 students were seriously injured in the collapse, and were among 67 people who were kept in hospital overnight after the collapse at one of Jakarta's landmark buildings.

A college student visiting the stock exchange said she felt a tremor just before the mezzanine floor collapsed into the building's lobby, with the debris hitting and injuring some of her friends.

"We were visiting the Jakarta stock exchange as part of our study tour when the structure suddenly collapsed, causing chaos," the student, identified as Ade from Palembang in Sumatra, told Metro TV.

She said some of her friends had head wounds and broken bones.

Floor collapse 'not because of a bomb'

Security stand near the collapsed floor inside the Indonesia Stock Exchange. ( AP )

The floor collapse was not caused by a bomb, national police spokesman Setyo Wasisto said.

The building is one of a two-tower complex which was targeted in a car bombing by Islamist militants in September 2000.

Dozens of police officials cordoned off the multi-storey complex as many people ran away and others were seen sitting on steps outside the lobby.

Sorry, this video has expired WARNING: Distressing content - Footage shows Jakarta stock exchange floor collapse

"The second floor of the building has collapsed," said Vindy, a personal assistant to exchange president Tito Sulistio, who was in the building at the time.

Megha Kapoor, who works in the building and was in the lobby at the time, said: "Slabs of concrete started to fall, there was lots of dust. Water pipes had burst."

"I heard a loud cracking sound. I saw a lady unconscious stuck under slab of concrete."

She said there had been a group of high school students on the level when it started collapsing.

Ceiling reportedly fell on crowded reception area

Images from the scene showed a mangled metal structure that had collapsed around a Starbucks cafe near the entrance to the building in the heart of Jakarta's business district.

TV images showed some people sitting on the steps outside the building.

Injured people are treated outside the Indonesian Stock Exchange building after the second floor collapsed. ( Reuters: Darren Whiteside )

The ABC's Indonesia correspondent Adam Harvey, who was about 50 metres away from the building's lobby, said it appeared the ceiling had fallen on a crowded reception area.

"There are many casualties inside and ambulances are attempting to get through to the building where it looks like there has been some kind of floor collapse," he said.

"You can hear a car honking.

"There is a wounded person in the back of the vehicle — that is a private vehicle with an ambulance stretcher in the back."

Injured people are evacuated from the Indonesia Stock Exchange. ( AP )

He said there were only a few rescue teams on site.

"Everyone is still arriving," he said.

"Another ambulance is leaving now with an injured patient."

Ambulances are seen following reports of a collapsed floor inside the Indonesian Stock Exchange. ( Reuters: Darren Whiteside )

Australians work in the building

Harvey said the building was in the heart of Jakarta's financial district.

"There are lots of western workers who work in this complex as well as many Indonesians," he said.

"There are Australians who work in this building, so we are just trying to work out what is happening.

"We don't really know what has gone on other than those reports that a floor has collapsed."

An image from 2015 shows the inside of the Indonesia Stock Exchange. ( Reuters: Nyimas Laula )

He said there had been no talk the incident was related to terrorism.

"I think it is probably safe to rule it out at this stage," he said.

"Building standards are an issue in Indonesia. This is not a new building. This has been here for a long time.

"There have been no recent earthquakes in Jakarta that might have sparked something."

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Jakarta police said they were seeking more information on the incident.

Stock exchange director Alpino Kianjaya declined to comment.

The stock exchange reopened for the afternoon session. All staff were safe, it said.

"100 per cent of bourse members are connected and safe. Bourse system is not affected," Mr Sulistio told reporters outside the building.

Stock exchange director Alpino Kianjaya declined to comment on the incident. ( Reuters: Iqro Rinaldi )

ABC/wires