German police commandos have stormed an apartment in the eastern city of Chemnitz and detained a second man in connection with a hunt for a Syrian refugee suspected of planning a bomb attack.

Key points: Police already questioning another man suspected of being involved in plot

Police already questioning another man suspected of being involved in plot Police confirm Jaber Albakr arrived in Germany in 2015, as part of wave of migrants

Police confirm Jaber Albakr arrived in Germany in 2015, as part of wave of migrants Several hundred grams of explosives found in apartment

"Nobody was injured and no shots were fired. We've taken the man into custody and we are questioning him now," said Tom Berhardt, spokesman for the Saxony state criminal investigation office.

Police found explosives in another apartment in the city that they raided on Saturday but have been unable to track down the suspect, 22-year-old Jaber Albakr.

German police have been searching nationwide for Mr Albakr, who slipped through their fingers as they were closing in on him, and have been questioning another Syrian man on suspicion he was involved in the plot.

The man in custody was one of three apprehended in Chemnitz on Saturday.

Mr Berhardt said the man in custody was the renter of the apartment that police raided in their search for the main suspect, Mr Albakr, from the Damascus area of Syria.

The other two men have been released.

He said the man in custody was Mr Albakr's "countryman," but would not give other details.

"We believe he is a possible co-conspirator," Mr Bernhardt said

Another man who knew Mr Albakr was taken into custody for questioning in a raid on his apartment.

As police prepared to raid the apartment building, Mr Albakr was observed leaving the premises.

Police fired a warning shot but were unable to stop him, Mr Bernhardt said.

They thought he had turned back into the building but was not the case, he said.

Mr Bernhardt also confirmed reports that Mr Albakr had come to Germany in the flood of 890,000 migrants who entered the country in 2015 and had been granted asylum.

Nobody was in the apartment when police SWAT teams blew down the door on Saturday, but investigators found "several hundred grams" of a volatile explosive hidden in the flat, enough to cause significant damage, Mr Bernhardt said.

"With this highly volatile explosive, even a few hundred grams is no trifle," he said.

"For an explosive of this type, it was a considerable amount."

German police asked local residents to remain indoors as they carried out their hunt. ( AP:Nonstop News )

Experts were still trying to determine whether it was the same explosive used in the deadly November 13 attacks in Paris and the March 22 attacks in Brussels known as TATP, or triacetone triperoxide.

"It's comparable to that," Mr Bernhardt said.

TATP has been used in many attacks over the years, and is favoured by violent extremists because it is fairly easy to make and detonate.

The explosives were destroyed in a controlled detonation by bomb squad experts in a pit dug outside the five-story apartment building, because they were considered too dangerous to transport.

The raid came after Saxony police were given a tip from Germany's domestic intelligence service that Mr Albakr may be planning an attack.

He had been on the agency's radar, but Mr Bernhardt said it was not clear how long.

AP/Reuters