The Jordanian government announced that toxic chlorine gas had escaped from an overturned container in the port of Aqaba in the south of the country on Monday.
According to authorities, hospitals are struggling to treat the many injured.
A spokesman for the Jordanian security authorities said a "container filled with toxic gas overturned during transport" at the port of Aqaba.
Footage on state television showed a container lifted by a crane falling.
A thick yellow cloud immediately escapes after impact.
People are fleeing the gas.
The southern part of the port was evacuated.
The head of the local health authority, Jamal Obeidat, called on residents to stay at home and keep the windows closed.
"Hospitals in Aqaba are already overwhelmed and can't take any more casualties," he added.
Appointment of a commission of inquiry
Prime Minister Bischer al-Hasawneh and Interior Minister Masen al-Faraja traveled to the scene of the accident, according to the Al-Mamlaka television station.
The government announced the formation of a commission of inquiry headed by al-Faraja.
The port of Aqaba is one of the most important on the Red Sea and Jordan's only seaport.
Most Jordanian imports and exports are handled through him.
The Israeli seaside resort of Eilat is only around five kilometers from the port of Aqaba.
However, a spokeswoman for the Israeli Ministry of Environmental Protection said the accident was probably less dangerous for Israel than for Saudi Arabia further south because of the wind direction.