A mosque in Perth's north has been fire-bombed overnight as the Islamic community marked a religious holiday.

Emergency crews were called to the Mirrabooka mosque just after 12am yesterday to find chairs and a tree on fire.

The blaze was quickly contained, but smoke and water badly damaged the second storey of the building.

No one was injured in the incident. Picture: 9NEWS (9NEWS)

Thousands of dollars worth of damage has been caused. Picture: 9NEWS (9NEWS)

It's understood the firebug struck while the Islamic community celebrated Eid al-Adha, the Festival of Sacrifice, but it remains unclear as to why the mosque was targeted.

Mosque leader Ameer Ali told 9NEWS he hasn’t had any trouble in three decades, and the community response is always positive.

“We run this place by weekly collections... the community is very helpful and that's why we've been running for 30 years,” Mr Ali said.

“Every Friday, something like 2000 people come to pray at this place. There have been no incidents so far, nothing happened.

“It's heartbreaking.”

Police at the scene this morning. Picture: 9NEWS (9NEWS)

Investigations are ongoing. Picture: 9NEWS (9NEWS)

9NEWS has been told six aerosol cans were seized by forensics at the scene today, with investigations ongoing.

It's estimated the repair bill could hit $250,000.