The continuing fatal siege on the troubled southern island of Mindanao in the Philippines could not be replicated elsewhere in the region, terrorism experts say.

The fighting in the city of Marawi has now entered its fifth week, a clear sign the government and the military in the Philippines were caught off guard and unprepared — as many as 300,000 residents are reported to be displaced.

Of the roughly 300 people reportedly killed, most are militants, but there are also dozens of military and civilians among the dead.

Associate professor Greg Fealy from the Australian National University told the ABC it would be highly unlikely a similar group could form in neighbouring countries like Indonesia, because the police and military would easily defeat them.

The south of the Philippines is considered as relatively lawless and a perfect ground for would-be jihadists. But Dr Fealy warns that the longer the battle continues, the deeper the consequences for the region.

"The more it embarrasses the Philippine army and the Philippine police, the greater the magnetic effect that kind of rebellion will be for Indonesian and indeed other Muslims across South-East Asia," he said.

It is believed as few as 40 Indonesians are in the Philippines, and an unverified number have been killed.

Terrorism expert Sidney Jones from the Institute for Policy Analysis of Conflict says the instructions from the Islamic State group leaders in the Middle East began to change midway through last year.

Smoke billows as government troops continue their assault against IS militants in the Philippines. ( Reuters: Romeo Ranoco )

"The message from Syria is that if it is getting too difficult to cross over, so if you can't get to Syria, go to the Philippines, and if you can't go to the Philippines, wage war at home," she said.

"And that message is coming through quite clearly it is almost as though in Syria the pro-ISIS structures there can't cope with more people coming through."

Graffiti is seen on a wall of a back alley in Marawi as soldiers battle on. ( Reuters: Romeo Ranoco )

Dr Jones said Indonesia, Malaysia and Singapore are deeply concerned by events in Marawi.

"I think the militants in the Philippines have shown an ability to withstand a military assault that far exceeds anything those countries expected," she said.

"I think they realised that more of their nationals are taking part than they expected."

Professor Fealy said more than 20 terrorist plots have been foiled in Indonesia since the beginning of 2016 and the main target remains police.

On the weekend, an officer was stabbed to death by suspected pro-Islamic State militants in Medan in North Sumatra — it came a month after three police officers were killed in a suicide bombing attack at a bus depot in the capital, Jakarta.

"The police are the enemy number one because it's the police who arrest and not infrequently kill terrorists," Dr Jones said.

Marawi jihadists could spread skills back home

Sorry, this video has expired There is growing concern the ultra-radical Islamic State group is gaining a foothold in South-East Asia (Pic: AP)

Foreigners also remain at risk, but they have not been targeted since the Starbucks bombing last January.

Since the beginning of May, Indonesian police have arrested 35 terrorism-linked suspects.

It is widely agreed that the biggest risk facing Indonesia will come from foreign fighters returning home from the Middle East and the Philippines with skills, including bomb making, that are currently lacked by those on the ground.

"Someone who has the combat skills and the leadership qualities to whip these not very professional people into shape," Dr Jones said.

"And that's why people have been so worried, first with people coming back from Syria, but now even more so with the fact people could come back from Marawi, from the Philippines, with the same skill set."

Dr Fealy said that the future looks bleak, especially if the militants' target shifts away from police and back to civilians and foreigners.

"If they did begin to do that there are actually lots of fairly soft targets for them, and we could see much worse death tolls in coming years," he said.