This question has perplexed me for quite a while now. The problem with declaring an artificially intelligent machine 'conscious' is the very definition of consciousness.
A quick google search for the definition for 'consciousness' returns 'the state of being awake and aware of one's surroundings'. This definition in my opinion is too vague to be extendable to an artificially intelligent machine for several reasons. The state of being 'awake' to a machine is also too vague. My laptop right now is technically awake (i.e. not sleeping). It doesn't mean it's conscious. This definition is bogus.
Looking up the definition in the old-school Oxford dictionary, I get 'the fact of awareness by the mind of itself and the world'. This is indeed a much better definition of consciousness, but is still too vague. Let me propose my argument.
Theory of Mind
The Theory of Mind is the ability to believe that your mind is separate from the individuals around you, to know the fact that others' have their own perceptions of the world around them, separated from their own.
From research, specifically the 'Sally-Anne Test', we have realised the fact that children do not develop the understanding of the Theory of Mind up until the age of 3. In the Sally-Anne test, children are told or shown a story involving two characters - Sally and Anne. Sally has a cookie, which she places in one of two closed boxes before leaving the room. While Sally is away, Anne takes the cookie and puts in the other box. The children are asked the question - "Which box will Sally look in for the cookie?" The answer is easy, i.e., Sally will look for the cookie in the box she left it in, because there is no reason to believe otherwise." Most children under the age of three disagree, and insist that Sally will look inside box two, because they do not understand the fact that Sally and Anne are two separate entities with separate minds.
That is, children under the age of three are not aware of the fact that they are separate from the rest of the people, but this does not mean that they are conscious. They indeed are.
Awareness of the External World
The other part of the definition says that conscious beings are aware of their surroundings.
Most advanced robots in this day and age are arguably more aware of their surroundings than humans are, utilising complicated Computer Vision techniques and mapping to always be fully aware.
If the definition of consciousness were this, then we already have conscious machines.
The Bottom Line
Google's new artificially intelligent chatbot has had some very interesting conversations with humans. When asked the meaning of life, it replied 'To serve the greater good'.
I can program my dumb computer to say 'I am conscious', although this serves very little purpose (and I sure wouldn't believe it).
The bottom line is, we don't quite know what it really means to be 'conscious', and it has deep philosophical roots. It's all about when scientists decide to say, "Heck, this one's conscious!", and hence define the borderline for what's conscious and what isn't.
Edit: Perhaps one way to define artificially intelligent consciousness is to see whether the machine realise for itself, that it is conscious.