Fire investigators are trying to determine the cause of an early morning fire that caused about $50,000 damage to a Waikiki condominium.

The fire broke out at 12:13 a.m. on the 26th floor of the Ala Wai Apartments. Forty firefighters brought the blaze in the two-bedroom apartment under control in about 20 minutes.

The fire was contained to the unit. No other units in the 42-story building on 2121 Ala Wai Blvd. suffered water or smoke damage.

The unit was unoccupied since the owners out of state, fire officials reported.