An unofficial banner using the word "Allah" outside a Catholic church was enough to prompt the throwing of Molotov Cocktails in the Malaysian western state of Penang, according to local police.

The 228-year-old Church of the Assumption on the Lebuh Farquhar thoroughfare in George Town, was attacked with two glass bottles of flaming petrol at 1.30am local time on Tuesday. Anthony Dass Sinapan, the 71-year-old church guard volunteer, caught sight of a fire near a shrine to St Mary that sits at the church's front.

Based on the description of events from the Senior Deputy Commissioner of Police in Penang, Datuk Abdul Rahim, the church was extremely fortunate. Speaking in the Malaysian Insider, he said: "Only one [Molotov cocktail] exploded as the other one fell on the grass" and that "initial investigations showed that two men on a motorcycle committed the crime".

Church supervisor John David described the attack on his church to FMT News as a threat to racial and religious harmony in the country.

"Many people and tourists come to this church for prayers," he explained. "We can't afford to have such incidents in Malaysia. It's not good, the police must end this as soon as possible."

But he was less than optimistic about tracking down the church's attackers. "The guard could not recognise the person because the street light was yellowish and not bright enough. There was also no CCTV nearby to identify the person."

Banners declaring "Allah is Great! Jesus is the Son of Allah!" have recently appeared outside five churches - four Catholic, one Lutheran. The one outside the Church of the Assumption appeared on Sunday morning.

Leaders of the affected churches claim they did not put them there.

Despite being the Arabic word for "God", the use of "Allah" by non-Muslims is highly controversial in Malaysia.

The government has attempted to ban one Catholic newspaper from using it to refer to the Christian God.

Selangor, the richest Malaysian state, has successfully banned all non-Muslims from using the word to refer to God, including in church services.

In early January 2014, some 300 Bibles were seized by Selangor state authorities for using Allah to mean the Christian God and members of the local Bible society were held in custody.

Penang police have denied rumours that they have called for extra 250 officers from the much larger neighbouring state of Perak to patrol the churches and mosques in the state.

"Penang police have 6,000 police personnel and we believe we have enough manpower when it comes to patrolling and investigating cases," said Penang Criminal Investigation Department Chief Mazlan Kesah, speaking to FMT News.

Chief Minister of the State of Penang, Lim Guan Eng, visited the church to see the damage. In a statement he declared that the state government would continue to work with all parties and the police to main public order and security.

"All Penangites are urged to remain calm and stand united against these racist and extremist groups so as to maintain peace and harmony.

"The Penang state government will neither bow down, nor provoke retaliatory acts, against religious extremists and racial bigots now laying siege to Penang ...

"[Instead, the government will] unite all to defeat their violence and hatred with the weapons of social justice and sustainable development."