Three people have been injured and thousands of people ordered to evacuate from surrounding cities and towns after explosions at an East Texas chemical plant.

Flames and smoke surged into the sky after the blast at the TPC Group plant in Port Neches, about 130 kilometres east of Houston, about 1am on Wednesday (local time).

The chemical fire continued to burn late into the morning, the Nederland Volunteer Fire Department said.

TPC officials said three workers were treated at hospitals after the initial blast and later released. All employees had been accounted for, they said.

Jefferson County Emergency Management coordinator Mike White told the Beaumont Enterprise that five residents had also been injured. They were being treated for minor injuries, mostly related to shattered glass.

The early morning blast also damaged homes and businesses.

From a nearby office, Kelly Berka saw the plumes of smoke from after the afternoon explosion.

“What a damned mess,” she wrote on Twitter. “We’re clearing out.”

Ms Berka later told CNN her co-worker, who lives near the plant, had her front door blown off earlier in the morning before evacuating.

Following a second explosion on Wednesday afternoon, local authorities ordered evacuations in a 6.5-kilometre radius that included Port Neches, Groves, Nederland and parts of Port Arthur.

The mandatory order threw the Thanksgiving holiday plans of thousands into disarray.

“Somebody in the path of the plume, if they feel any irritants or have any respiratory conditions or allergies, it’s in their best interest to go to a relative’s home or a friend’s home and get out of that wind direction,” Jefferson County Judge Jeff Branick said.

“We think people ought to use just good ol’ common horse sense because emergency personnel are too busy to try to enforce these things.”

Jefferson County Sheriff’s Office captain Crystal Holmes told CNN the fire was “contained and not going anywhere but it’s not under control”.

The Port Neches Police Department said there had been “extensive damage” in the local area.

“Please stay off the roads anywhere near the refineries,” it said in a statement.

“Obey all the barricades that are in place. We are doing everything we can to keep everyone safe and informed.”

#BREAKING: All of Port Neches and Groves under a mandatory evacuation. @12NewsNow pic.twitter.com/3RyN8u2vaw

— Lauren Hensley (@LaurenHensleyTV) November 27, 2019

The fire is burning a chemical called butadiene, a colourless gas that is considered a health hazard, according to the US National Library of Medicine. It is made from processing petroleum and is used to make synthetic rubber and plastics.

TPC health safety and security director Troy Monk said he had also woken to his front and back doors being blown into their frames.

He said the initial focus of emergency work was on containing the blaze and keeping surrounding storage tanks cool. The next priorities would be putting out the fire, then investigating its cause, he said.

Mr Monk said about 30 staff were on site at the time of the explosion.

-with agencies