A family of alleged Islamic extremists are accused of planning to bring down a passenger plane in an ISIS-inspired terror attack in Australia.

Two Lebanese-Australian father and son duos are reportedly the four men arrested over the alleged plot after dramatic raids across Sydney on Saturday afternoon.

While the full extent of the alleged conspiracy is not yet known, the men may have planned to detonate a homemade bomb on a flight from Sydney to the Middle East, possibly Dubai, Seven News reported.

A kitchen mincer is believed to be among the everyday items the alleged attackers used to form a lethal device, according to the Herald Sun.

The apparatus was reportedly 'ready to go' as counter-terrorism police stormed properties across the city's west and inner-east.

There are also reports they had allegedly plotted to gas passengers aboard an aircraft in a plan orchestrated by ISIS militants in Syria, according to The Australian.

The paper was told the four, who are all related by blood and marriage, allegedly made a 'non-traditional' device designed to kill passengers with a sulphur-based gas.

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Two father and son duos are reportedly the four men accused of plotting to bring down a plane departing from Sydney with a homemade bomb. Pictured, one of the men is detained by police

One of the accused is pictured with a bandaged head following his arrest on Saturday night

Australian Federal Police at the check-in at Sydney Airport on Sunday as part of heightened security measures across the country

Police standing by at Sydney Airport on Sunday following the dramatic raids on Saturday afternoon

The accused, whose names are known to Daily Mail Australia but not yet confirmed by police, were arrested in the simultaneous raids.

Australian Federal Police, ASIO and NSW Police jointly carried out the operation on Saturday in Surry Hills, Lakemba, Wiley Park and Punchbowl.

One of the men was reportedly dragged from his Lakemba home wearing only a towel, while his father was arrested at a property in neighbouring Punchbowl.

The other father and son duo are understood to have been arrested in separate raids.

Counter terrorism police (pictured) stormed four Sydney properties and arrested four men including one man (pictured) at Surry Hills after being alerted to an alleged plot to bring down an plane with a 'bomb'

Police are seen continuing their investigations in the aftermath of the Sydney terror raids

Long queues and waits were expected following a thwarted alleged terror threat on Saturday

The counter-terror raid in Surry Hills (pictured) took place just metres from the Redfern Mosque (pictured)

One man draped in a bed sheet with a heavily-bandaged head was seen being led into an ambulance outside a Surry Hills property.

The man appeared to be distressed and bleeding from the head as he walked to a waiting ambulance, Nine News reported.

He could be heard saying 'they bashed me.' When asked by who, he answered 'police.'

When asked why he was being arrested, the man mumbled 'I don't know nothing.'

Shocked neighbours have said the family living in the property were 'perfectly nice and normal people.'

'We knew them to say hello to and they seemed nice,' said one woman, who didn't want to be identified.

The woman, who lives at the back of the property, said an elderly couple lived in the home and had adult children.

AUSTRALIAN TERROR PLOT FOILED: THE ALLEGATIONS What was the plot? The group allegedly planned to use an improvised device to bring down an aeroplane in an Islamist-inspired conspiracy. Police say they have limited information so far about the date, location or specific strategy involved. What happened during the raids? NSW and Federal Police swooped on five properties in the Sydney suburbs of Surry Hills, Lakemba, Wiley Park and Punchbowl on Saturday afternoon and found a 'considerable' amount of material. But police won't say if they discovered an actual explosive device. Could it have happened? AFP Commissioner Andrew Colvin said they treated the plot as credible and there was an intention and 'quite possibly a capability' to carry it out. However, he also said there was no reason to believe security at Australian airports has been jeopardised. What happens now? The arrested men haven't yet been charged. Police say their searches at four of the properties are ongoing and could take 'many more days' as they gather enough evidence to support charges. What's changing at airports? Travellers have been told to arrive two hours earlier to make allowances for increased scrutiny. They may notice "intensified" security procedures, but some bolstered arrangements will happen behind the scenes. Travellers have also been asked to limit baggage to make things easier. Advertisement

Forensic teams (pictured) and the bomb squad attended the scene during the Surry Hills raid

Prime Minister Malcolm Turnbull has told the public not to panic and to inform police (pictured) of any suspicious activity

Police said raids took place in the suburbs of Surry Hills, Lakemba, Punchbowl, and Wiley Park

Residents living near the Surry Hills home, just metres from the Redfern Mosque, were evacuated while the bomb squad worked to remove the 'explosive device.'

One neighbour of a man arrested in Wiley Park told The Daily Telegraph the accused would nurture stray cats in the area.

'He and his brother would feed about 15 cats and when we complained that they were bringing ticks and diseases into the block, they would walk off,' they said.

Relatives of two of the accused spoke out following the arrests, saying they 'love Australia.'

The four men arrested for their alleged role in the conspiracy can be detained for up to a week while investigators comb through evidence.

A magistrate ruled police can hold the men for an 'additional period of detention' under the Crimes Act while investigations continue.

'This recognises that terrorism investigations are inherently complex and that there can be legitimate reasons for extended periods of detention for suspects in such matters,' an AFP statement said.

Airports across Australia are experiencing long queues, with frustrated travellers vented their anger on social media

Passengers waiting after long queues formed following heightened security at airports

Police on the scene in the Lakemba area following the aftermath of the Sydney terror raids which resulted in four arrests

A number of 'items of interest' were seized in the raids and searches continued on Sunday, with AFP Commissioner Andrew Colvin suggesting they may take 'many more days'.

The plan involved an improvised device and was Islamist-inspired, he added.

'We've taken this threat very seriously,' Mr Colvin said.

'You should infer that we think this was credible and there was an intention, and there was quite possibly a capability as well.'

Airports across Australia are experiencing long queues after Prime Minister Malcolm Turnbull warned of heightened security measures across the nation.

He said the raids were a 'major joint counter-terrorism operation' and reminded the Australian people 'the threat of terrorism is very real'.

'The office of transport security has advised security screening will take longer, and travellers should arrive at terminals at least two hours before flights to allow ample time for screening,' he said on Sunday.

Travellers turned to social media posting photos of massive queues leading into customs at Sydney Airport and passengers tweeting to not underestimate the wait.

'Not sure I agree with the ''creation'' of a mass gathering ''before'' security screening -closed screening stations,' one traveller tweeted.

Police officers continue their investigation in Lakemba following raids on Saturday afternoon

Police found an 'explosive device' and part of Cleveland Street (pictured) in Surry Hills was cordoned off

'Long queues at Sydney Airport - paranoid security state in full regalia,' another wrote.

Some passengers were warning others to add an extra 30 minute travel time onto the already extended period.

'T3 Sydney airport a mess. If you are flying come very early,' another social media user wrote.

Prime Minister Turnbull reiterated the raids were aimed at stopping an alleged terror plot to 'bring down' a plane and said security screening will take longer over the coming days.

'Some of the measures will be obvious to the public, some will not be - those travelling should go about their business with confidence,' Mr Turnbull said.

Police are pictured as they continue their investigations into the terror raids on Sunday

Australian Federal Police are pictured on Sunday in the aftermath of the Sydney terror raids

Australian Federal Police Commissioner Andrew Colvin (pictured) said details of the alleged terror plot are still emerging

'The office of transport security has advised security screening will take longer, and travellers should arrive at terminals at least two hours before flights to allow ample time for screening.

'They should limit the amount of carry-on and checked baggage, as this will help to ensure that security screening is efficient.'

Virgin Australia released a statement on the extra security.

'Passengers should arrive at least 2 hours before domestic flights and 3 hours before international flights to allow time for security screening,' the statement read.

Prime Minister Malcolm Turnbull (pictured) said for those travelling on planes to allow extra time for heightened security measures on Sunday

Australian Federal Police are seen at a property in Lakemba in Sydney's west on Sunday

Cleveland Street was cordoned off and shouting and screaming was heard as a man was led away by police

'Passengers should limit the amount of carry-on and checked baggage they travel with as this will help to ensure security screening is efficient.'

New South Wales Police confirmed that the four men in custody were yet to be charged.

Australia's terror threat remains at probable.

Prime Minister Turnbull released a statement on the raids, confirming the involvement of the Australian Federal Police, ASIO and NSW Police.

Australian Federal Police on Sunday leaving a property after the dramatic terror raids

Cleveland Street (pictured) was closed between Elizabeth St and Young St, and Goodlet Lane was also closed

Residents living near the Surry Hills home were evacuated while the bomb squad worked to remove the 'explosive device' and forensics (pictured) examined the scene

'These operations are designed to disrupt and prevent plans to undertake terrorist attacks in Australia,' the statement said.

'My number one priority, and that of my government, is the safety and security of all Australians.

'The public should be reassured that our security and intelligence agencies are working tirelessly to keep us safe.'

Mr Turnbull urged people to call the National Security Hotline on 1800 132 400 if they see or hear anything suspicious.

Goodlet Lane in Surry Hills (pictured) was closed while police examined the scene of the raid

Police involved in the raid were acting to prevent an alleged plot to bring down a plane with a 'bomb'

An 'explosive device' was discovered at the Surry Hills (pictured) property and deactivated by a bomb squad that was called to the scene