AUSTRALIANS heading to Indonesia have been told to reconsider theirtravel plans because of a very high threat of further terrorist attacks.

The Department of Foreign Affairs and Trade (DFAT), in an updatedtravel advisory, said Australians should specifically avoid travel todowntown Jakarta near the Ritz-Carlton and JW Marriott hotels that weretargeted with bomb blasts on Friday.

An Australian man has reportedly been injured in the explosions that rocked two international hotels in Jakarta.

At least six people, including several foreigners, have been killed and 10 injured when explosions ripped through two luxury hotels in downtown Jakarta on Friday, police say.

Bombs exploded at the Ritz-Carlton and Marriott hotels in the Indonesian capital, ripping the facade off the Ritz and killing at least six, police say.

One hospital emergency room said it was already treating 15 people.

Debris and shattered glass littered the street outside, and ambulances were being shuttled into the area.

Alex Asmasubrata, who was jogging by the hotels, said he first heard a loud explosion at the Marriott. Five minutes later, a bomb followed at the Ritz. He saw four bodies inside the Marriott, including one with its stomach blown out.

Witnesses said they saw injured people being evacuated by car from the Ritz-Carlton hotel in the upscale Mega Kuningan business district in the centre of the city.

Police sealed off the area near the hotels, an AFP correspondent said. Windows had been blown out of a second-storey restaurant at the Ritz Carlton.

"I heard two sounds like 'boom, boom' coming from the Marriott and the Ritz-Carlton. Then I saw people running out," security guard Eko Susanto told AFP.

Witness Intan told TV One one of the explosions wrecked the lobby of the Plaza Mutiara building.

"I was having breakfast on level 16, I heard an explosion and went down to the first floor and it was a mess. I saw foreigners all bloody, about three to five of them, badly wounded," she said.

The explosions rocked the area around 8am local time (1100 AEST).

"I saw some people being carried into a Mercedes. There was a lot of them in there, they were having trouble closing the doors," a witness, who gave her name as Mery, told ElShinta.

The Marriott hotel was attacked in 2003, when 12 died. Southeast Asian terror network Jemaah Islamiah was blamed in that blast.

DFAT said it continued to receive credible information that terrorists could be planning further attacks in Indonesia with Bali remaining an attractive target.

"We advise you to reconsider your need to travel to Indonesia, including Bali, at this time due to the very high threat of terrorist attack," DFAT said.

"If you do decide to travel to Indonesia, you should exercise extreme caution."

DFAT said Australians in Jakarta requiring consular assistance should contact the Department of Foreign Affairs and Trade on + 61 2 6261 3305.

Australians with concerns for family or friends in Jakarta should first try to contact them directly.

If they can't be contacted and there are fears for their safety, DFAT's emergency centre can be contacted on 1300 555 135.

Read what people are saying about the explosions on Twitter.