AAP understands the journalist was hit by a stray bullet, rather than a targeted attack.
Harvey posted a picture to Twitter of an X-ray showing the bullet lodged in his neck, with the caption "Lucky".
He said he initially thought he had been hit by shrapnel in what was considered a relatively safe compound some way away from the fighting.
"We were joking about it a few minutes later but it turned a bit more serious when I saw the X-ray," he said.
Harvey said the Marawi hospital he was being treated in came under attack while he was there, with gunfire heard outside the building.
The journalist's sister, Claire Harvey, told 2GB radio her brother would need surgery, which she hoped would occur in Singapore.
"It looks like this bullet has got him in the gap between the bottom of his helmet and the top of his (protective) vest," she said.
An ABC News spokesman said Harvey was receiving medical treatment for the injury, which was described as not serious.
A video uploaded by Filipino radio station DDZB Super Radyo showed the journalist wearing a neck brace and helmet while being mobbed by local reporters.
"I've just gone to get an X-ray to get it checked out," Harvey said in the video posted on Twitter by the station.
Harvey, who is the ABC's Jakarta correspondent, was within the Provincial Capitol Compound taking photos of evacuees.
It was considered to be a safe zone and he was wearing protective gear.
Less than 24 hours before he was shot Harvey had tweeted how he came across a killing on the drive out of Marawi, which is 830km south of the capital Manila.
"Brutal times in the Philippines," he said in the tweet.
Marawi is a city that has been hit by a series of violent incidents in recent weeks between a local gang aligned with the Islamic State and Philippines security forces.
As many as 1500 civilians are trapped in the Isis-held parts of Marawi.
The Philippines military confirmed that US troops were on the ground near Marawi City but are not involved in fighting the Islamist militants.
The military had previously said the US was providing technical assistance to end the occupation.
