Colleyville police confirmed the information just before 10 p.m. local time.
At least four hostages, including a rabbi, were taken earlier on Saturday at Congregation Beth Israel in Colleyville, just outside Fort Worth. No injuries were reported among the hostages, one of whom was released earlier in the evening.
A man reportedly took the hostages after entering the Congregation Beth Israel synagogue in Colleyville, Texas - near Fort Worth - during a religious service around 11.30am on Saturday. The service was being live-streamed.
It is unknown how many hostages the man has at the moment.
He reportedly demanded that a relative in prison be released.
Colleyville, Texas, police are conducting SWAT operations and locals are being told to evacuate the area. State police are also assisting the scene as authorities set up by a nearby middle school, according to WFAA. The school is around the corner from the synagogue.