A team of chemical experts is looking into what caused two massive explosions in Tianjin, northern China.
Rescue workers and the Chinese army are continuing to try to make the area safe.
Fires are still burning where two blasts happened at a warehouse used to store hazardous goods, including chemicals.
At least 50 people have lost their lives and more than 700 people are known to have been injured.
A team of military chemical experts is testing for dangerous gases at the scene and rescuers have been ordered to wear protective clothing.
The investigators are still working out exactly what happened, but it's thought the explosions were not caused by terrorists.
'Seen from space'
The blasts caused a huge fireball that could be seen from space and the impact could be felt from several kilometres away.
Buildings have been destroyed and many people have had to leave their homes.
Soldiers have been clearing roads and putting up tents to help people who have lost their houses.
Search teams have been working hard to help the people affected.
According to news reports in China they found a survivor in the rubble on Friday - a 19-year-old fire fighter called Zhou Ti.