Over two dozen people are feared killed in southwestern United States after a gunman opened fire at a church outside San Antonio, Texas, on Sunday, U.S. media report.

The mass shooting reportedly occured at First Baptist Church of Sutherland Springs, Texas, about 30 miles southeast of San Antonio, reports said.

Fox News quoted Larry Wiley, commissioner of Wilson County, as confirming that between 20 and 24 people are dead, and around 20 were wounded in the attack which occurred at about 11:30 a.m. on Sunday.

The attacker, whose identity is still being verified by authorities, was shot dead at the scene, reports said.