LA PORTE, Texas (AP) — A federal agency that investigates chemical accidents has announced that it will send a team to a Houston-area industrial plant where a chemical leak killed four people.

The U.S. Chemical Safety Board said Saturday night that it is sending seven people to the DuPont plant where the leak of methyl mercaptan killed four employees and hospitalized another.

The leak began around 4 a.m. Saturday and was contained about two hours later. The cause of the leak was not immediately clear.

DuPont said the chemical was used at the plant to create insecticides and fungicides.

Several employees had responded to the leak when they were exposed to the chemical, plant manager Randall Clements said in a statement.

"There are no words to fully express the loss we feel or the concern and sympathy we extend to the families of the employees and their co-workers," Clements said. "We are in close touch with them and providing them every measure of support and assistance at this time."

A fifth worker was hospitalized and being held for observation. That worker's condition was not immediately known, and none of the victims was immediately identified.

Clements said DuPont would be cooperating with local, state and federal officials investigating the leak.

"As part of that investigation, we are conducting our own top-to-bottom review of this incident and we will share what we learn with the relevant authorities," he said.

Jeff Suggs, emergency management coordinator for La Porte, said the chemical release was not toxic for those living nearby, but that it caused a smell that's similar to rotten eggs.

"It's a nuisance smell in the area. It's a smell that's traveled quite far," Suggs said.

Methyl mercaptan is also commonly used to odorize natural gas — which has no odor — for safety purposes.

The La Porte plant has 320 DuPont employees. Four other companies are also tenants at the complex.