Northern Ireland police say two officers have escaped injury after two pipe bombs were thrown at their vehicle after they responded to a bogus emergency call.

No group claimed responsibility for Tuesday's ambush in an Irish Catholic part of north Belfast. But Irish Republican Army splinter groups regularly target police as part of their efforts to undermine Northern Ireland's peace process.

A senior policeman, Chief Inspector Andy Freeburn, says it was "sheer good fortune" that both officers were not killed or wounded.

The officers reported two distinct blasts as they stepped out of their vehicle shortly after midnight.

Police sheltered local residents overnight in a nearby gymnasium. The road remained cordoned off Tuesday morning as forensics officers collected bomb remains for analysis and searched the area for potential unexploded devices.