A woman was killed in Texas' Houston on Sunday -- on a day the majority of the US brimmed with anticipation for Super Bowl LVIII -- after opening fire at a megachurch run by prominent evangelical Christian pastor Joel Osteen, the city's police chief said.

Two people were shot during the shooting. Among them, a child aged about five is in critical condition while a 57-year-old man shot in the hip is stable, said Troy Finner -- the city police chief.

In a post on X late in the afternoon, Lakewood Church said there was an active shooter situation that included shots being fired and law enforcement arriving on the scene.

The woman -- in her early 30s and wearing a long trench coat, holding a long rifle and a backpack -- entered the church, accompanied by a boy, believed to be about five years old, and started shooting, Finner said.

Two off-duty law enforcement officers who were at the church when the shots were fired at 1.50 pm opened fire and killed the woman, he added.

The woman's identity has not yet been revealed.

If law enforcement gunfire is responsible for striking the child, Finner said "I'm going to put that blame on her" for putting the boy in danger.

At the press conference, Osteen said he would pray for both the victims and the shooter, saying he was grateful the shooting happened between services when fewer people were in the building.

The police believe the shooting was an isolated incident and there is no further danger to the public.

The woman threatened that she had a bomb and sprayed an unknown substance as first responders arrived, the police chief said.

It is still not clear what the substance was, as fire department personnel arrived to investigate and clear the scene, he added.

The police checked a vehicle and backpack for possible explosives but none have been reported.

Houston Mayor John Whitmire lamented that the violence took place while people were preparing to practise their faith and others looked forward to the Super Bowl encounter between the San Francisco 49ers and the Kansas City Chiefs.

"We find ourselves gathered here to respond to this tragedy," he said.

In a statement, Governor Greg Abbott said, "Our hearts are with those impacted by today's tragic shooting and the entire Lakewood Church community in Houston. Places of worship are sacred." Abbott said he offered "full support and resources of the State of Texas" to Whitmire "to help this community and help bring swift justice to the criminal who committed this crime".

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