If a customer approaches you while you are in the middle of a high-priority task, what do you do?
A client is equally important as a priority task so ignoring a client's problem can put you in trouble too. But your focus should be tilted towards the high-priority tasks. You can escape this problem by just asking for help from your colleague.
I would help the client if the query can be resolved instantly and verbally otherwise I will ask my coworker's help to deal with the client's query.