CORPUS CHRISTI, Texas — A dredging vessel at a Texas port hit a natural gas pipeline Friday, sparking an explosion that sent six people to the hospital and left four others missing, authorities said.

The explosion happened at about 8 a.m. in the Port of Corpus Christi when the dredging vessel Waymon L Boyd struck a submerged pipeline, Coast Guard Lt. Marina Lawrence said. The Port of Corpus Christi said in a statement that it was a natural gas pipeline.

Initial reports indicated about 18 workers were in the area at the time, according to the county’s top elected official, Nueces County Judge Barbara Canales. Four of those people were missing, six were taken to hospitals and eight were uninjured, she said. Of the six injured, five were airlifted to a San Antonio hospital for severe burns while another was expected to be discharged Friday, said Sean Strawbridge, CEO of the Port of Corpus Christi.

Corpus Christi Fire Department Chief Robert Rocha said that upon arrival, firefighters “encountered heavy fire and smoke conditions.” By late Friday morning, the supply line feeding fire had been shut off, Rocha said.

The fire was extinguished Friday afternoon, Strawbridge said.

Gov. Greg Abbott issued a statement saying that the state was working closely with authorities in the area. The National Transportation Safety Board also said it is investigating.