FELDA SAHABAT, Malaysia: Malaysia Wednesday escalated its hunt for armed Filipino invaders who dodged a military assault meant to crush them, as a Philippine guerrilla warned more fighters had arrived.

Malaysia's police chief said followers of a self-styled Muslim sultan had scattered after an air and ground attack Tuesday on their stronghold in eastern Sabah state, aimed at ending the country's worst security crisis in years.

Authorities had "expanded the operations area", Ismail Omar told reporters in Felda Sahabat, a village about 15 kilometres (nine miles) from the site of the three-week stand-off.

He said the expansion was necessary as invaders were on the move, giving no details, but adding that one gunman was believed killed in an early morning exchange of fire.

However, he declined to answer reporters' questions on whether any of the estimated 100-300 militants had been captured or confirmed dead.

The armed group arrived in the Malaysian state of Sabah on Borneo island from the adjacent southern Philippines on February 12, claiming it for their "sultan" and tearing open a long-dormant territorial row.

After an initial stand-off in the sleepy farming village of Tanduo, two shootouts erupted there and in another town in recent days, which together with related violence has left 19 militants and eight police officers reported dead.

Following the shootings, Malaysia on Tuesday launched an attack on Tanduo with jet fighters and soldiers.

But their leader, Jamalul Kiram III, appeared to thumb his nose at Malaysia Wednesday, saying in Manila that he had just chatted by phone with his younger brother, one of the incursion's purported leaders.

"He was telling me they are eating good food, but the hard thing is they are being chased. So where will they go?" he said, declining to specify their location, but adding that they would not surrender.

Kiram, 74, is the self-proclaimed heir of the former sultanate of Sulu, which once controlled part of the southern Philippines and claimed sovereignty over Sabah. The intruders are attempting to reassert his authority there.

A leader of the Moro National Liberation Front (MNLF), which waged a past insurgency against the Philippine government, said hardened fighters from his Muslim group had arrived to support the militants.

"Many have slipped through the security forces" in recent days, Muhajab Hashim told AFP in Manila, adding more were expected to join the fray, but declining to reveal numbers.

"They know the area like the back of their hands because they trained there in the past," he said, referring to long-standing allegations that Malaysia helped trained MNLF leaders for their insurgency against Manila.

Muslim-majority Malaysia, accustomed to watching neighbours Thailand and the Philippines grapple with Islamic insurgents, has been shocked by the drama.

The government, which faces closely fought elections in coming months, has been harshly criticised over the breach and for appearing to dither.

The news that militants remained on the loose stoked the fears of local residents already on edge over the stunning incursion into their remote corner of Borneo island, which is covered by vast oil palm and other plantations.

"If there are no more negotiations I think more people on both sides will die," local resident Shamsul Bahari said.

"I am scared to even go to work in the palm oil estate."

An AFP reporter saw eight military trucks full of soldiers in full battle gear heading toward Tanduo Wednesday from Felda Sahabat, the nearest point to the trouble-spot that authorities are allowing outsiders to reach.

The trucks were followed by two armoured personnel carriers.

Authorities have not explained how the intruders were able to slip through a security cordon in place for three weeks.

Britain, the United States and Australia issued advisories warning against travel to affected areas.

Some suspect the MNLF orchestrated the offensive because they feared a peace deal being finalised between the Philippine government and another Muslim separatist group would marginalise them.

Philippine presidential spokesman Edwin Lacierda told AFP its navy intercepted 70 people last month trying to join Kiram's followers from the Muslim southern Philippines.

He said the government had no knowledge of Hashim's claim of MNLF fighters on the way.