At least nine people have been killed and as many as 160 injured in a massive blast outside the Australian embassy in Indonesia's capital, Jakarta.
Security guards or passers-by may have been killed in the blast
Jakarta's police chief said a suicide car bomb may have caused the blast, and linked it to bomb expert Azahari Husin.
Da'i Bachtiar said it was similar to those used on the city's Marriott Hotel last year and Bali nightclubs in 2002.
It bore the hallmark of militant Islamists Jemaah Islamiah (JI), widely blamed for both attacks, he said.
The BBC's Rachel Harvey says the attack left a large crater in the ground and damaged nearby buildings and vehicles.
Azahari Husin, a British-trained Malaysian engineer and one of Asia's most-wanted men, is suspected of playing a part in building both devices.
Appeal for calm
Indonesian President Megawati Sukarnoputri broke off a visit to Brunei where she was attending a royal wedding, flying to the scene of the blast and visited local hospitals.
"[I] hope that all Indonesians will remain calm and will not get panicked. Certainly, those
who do not want the election to succeed want us to get panicked," she said in a televised statement before her return.
The second and final round of the country's presidential elections are due on 20 September.
Until now security and terrorism have not been major campaign issues, but that will almost certainly change now, our correspondent says.
Australian Foreign Minister Alexander Downer said the attack was targeted at his country.
"It was outside the Australian embassy, you would have to conclude that it was directed towards Australia," Mr Downer said in Adelaide before leaving for Jakarta.
Prime Minister John Howard said all Australian embassy staff had survived though some local employees remained unaccounted for.
All the dead were Indonesians.
The blast happened at about 1030 local time (0330 GMT) in the southern district of Kuningan.
One witness said he may have seen the vehicle that was used in the bombing.
"Before the bomb blast, a mini-van car intentionally hit the road divider which was placed in front of the embassy's gate," Ismanto, an embassy security guard, told Indonesia's Antara news agency.
Our correspondent says the embassy itself, in one of Jakarta's most exclusive and busiest business districts, is well protected by a security fence. But an Australian spokesman said the building sustained "serious" damage.
The centre of the blast was the road just in front of the embassy, but office blocks on either side were severely damaged.
INDONESIA'S WAVE OF TERROR
December 2000 - Church bombings kill 19
October 2002 - Bali attacks kill 202, many Australian
December 2002 - Sulawesi McDonald's kills three
August 2003 - Jakarta Marriott Hotel bomb kills 12
September 2004 - Bomb outside Australian embassy in Jakarta
Plumes of smoke could be seen rising into the air above the site. There were gaping holes where windows were blown out. Glass, concrete and metal lay strewn across the ground.
Mangled remains of vehicles littered the area, many apparently lifted into the air by the force of the blast.
Our correspondent says Western embassies recently raised their security alerts, citing credible intelligence that an attack on Jakarta was planned.
Indonesia's financial markets went into a tailspin after news of the attack emerged, falling about 4% but later recovering.
The blast also came exactly a month before Australia's general election on 9 October, where terrorism is already a campaign issue.