Image copyright China National Earthquake Network Image caption The first blast registered as equivalent to detonating three tonnes of TNT

The blasts in Tianjin on Wednesday night were so large that they registered as seismic activity in China.

An official from China's National Earthquake Network told the BBC that scientists were "alarmed" at the scale of the explosions. The official confirmed that:

The shockwaves from the first explosion were equivalent to detonating three tonnes of TNT

The magnitude that followed the second explosion was seven times that from the first one: equal to 21 tonnes of TNT

The force of the blast was felt many kilometres away from the warehouse where the explosion took place in the port city and residents registered their horror at the scale of the explosions.

Image copyright China National Earthquake Network Image caption The second explosion was seven times as powerful as the first

"The impact alone woke me and my sister up last night, we were so scared. We hid under our blankets and were wondering if it was an earthquake or atomic bomb. My thoughts and prayers go out to all the deceased," one Weibo user said.

"I was sleeping when our windows and doors suddenly shook as we heard explosions outside. I first thought it was an earthquake," Reuters news agency quoted one resident Guan Xiang, who lives 7km (four miles) away from the explosion site, told the Reuters news agency.

According to the China Earthquake Administration's official account on Weibo, the first explosion was registered at a magnitude of 2.3 and the second at 2.9.

Even the United States Geological Survey registered the explosions as seismic events. The Guardian newspaper quotes USGS geophysicist John Bellini as saying that it is rare to detect seismological activity from events such as the Tianjin explosion.

Reporting by Heather Chen.