Is a hotel responsible for lost goods when cleaners have entered a locked room to clean and goods have gone missing?

That's why it is recommended to take out travel insurance when one travels. It is also common practice to keep valuables secured away. 

Some of the more up market hotel usually have a small safe in the closet area. 

The hotel I have stayed at in Sydney has them.

No, otherwise they would be scammed out of money by people like you. 

Parking garages even have a notice that they are not there to give you money as well. 

There would be too many lawsuits for this crap.

Claim on travel insurance and also contact the cops about this the Hotel will have to allow them to view the security camera footage.. You will probably need a police report for your insurance claim. 
Also go online and write a review regarding the hotel and what happened.

No, the hotel is not responsible. It is the guests responsibility to secure any valuable items by either taking these from the room when they go out or leaving the valuables in the hotel safe at reception. 

If something has been stolen you can report this to police, and try to claim on your travel insurance.

In addition to what's above, the hotel safe is barely big enough for my wallet and digital camera let alone my laptop which is what was stolen. We were told our room would not be cleaned during our stay but coincidentally the laptop was stolen the day the cleaners decided to clean our room. There were no signs of forced entry and the room was entirely locked both when we left and when we arrived. The hotel so far is refusing to look at cctv let alone giving us access (due to privacy).

You shouldn't leave valuables in a hotel room. Can you prove you even had them? 
Hotels have been scammed over non-existent valuables so many times that they tell you to put valuables in the safe. 
You didn't? Bad luck. No claim.

I worked front desk n these awful "guests" bitched at me for when things went missing (yea...because of course I had to have taken it because I'm standing here all damn day long!) and housekeepers would be crying when they were berated in the hallway: "this watch costs more than you make in a year!"...a*holes