Hungarian police are searching for a suspect believed to be behind a homemade shrapnel bomb blast in central Budapest on Saturday that seriously wounded two police officers, national police chief Karoly Papp said.

"We consider this attack occurred against the entire Hungarian police. Someone tried to execute my officers," Papp told a news conference on Sunday.

The blast went off shortly after 10:30 pm local time along one of the Hungarian capital's busiest streets, blowing out a store front and damaging nearby buildings and cars.

The two officers needed surgery, with the male officer in stable condition and his female colleague in a critical condition.  

Several hundred officers and investigators are working on finding the culprit, who police believe to be a 20-25 year-old male who was wearing blue jeans and a hat.

"We will find the perpetrator and discover his motivation," Papp said, adding there was a 32,690 euro ($36,700) award for information leading to the suspect's arrest.

Investigators are working on "seven possible versions" of what happened, Papp said, not ruling out terrorism as a motivation.

The mysterious bomb blast comes ahead of an October 2 referendum on the European Union's plan to share and relocate migrants.

Prime Minister Viktor Orban, a hard-line critic of the EU's migration policy, called the referendum to "send Brussels a message" that it could not dictate to member states a Europe-wide migration policy.

The vote comes amid concern in Europe over migrants and security.

A Hungarian opposition party called on the police to release details of the blast as soon as possible so that the government doesn't try to use the blast to stoke fear and gain political points.

cw/rc (AFP, AP, Reuters)