Vehicles parked in the north of town have been targeted by thieves over the past few weeks with valuables such as Ipods, phones and money stolen.
Police said criminals were forcing their way into cars between 4am and 6am.
Several vehicles had also been left unlocked and officers are urging owners to make sure their cars are secure.
Inspector Sarah Leadbeatter of Horsham district prevention team, said: “Some of the vehicles entered were insecure and I would urge all owners to double check their vehicles are locked and secure before leaving them unattended.
“This applies even when they are left on private driveways or in private car parks and even if they’re only left for a few minutes. Remember to take any valuables with you and don’t leave handbags, money or electronic devices on show.”
As a result police said more early morning patrols had been launched.
Anyone who witnesses any suspicious activity around vans and cars, is asked to contact police on 101 or online at our website www.sussex.police.uk