On August 10, 2016 an employee was charging his mobile phone in his office and in the process the phone exploded and caught fire. He quickly disconnected the charger from the power source and put the fire under control.
It's not uncommon to hear about a phone exploding or bursting into flames during charging. There are instances where android phones caught fire and burnt down a whole building.
More often than not, the event is caused by one of two factors: either the battery or the charger is not the original product.
Lithium batteries can suffer from a problem called thermal runaway. That is to say, heat causes an uncontrollable heat generation resulting in overheat. Because of this, they are equipped with a system that protects against overcharging and prevents hazardous reactions of the chemicals contained within. A lesson learnt from this is that we should not leave batteries to be charged when we are not around or we should not leave batteries to be charged overnight.