Mbeketoni eywitnesses say Al-Shabaab gunmen executed men in front of their families and killed others who had gathered to watch World Cup football on television.
"The attackers were so many and were all armed with guns. They entered the video hall where we were watching a World Cup match and shot indiscriminately at us," Meshack Kimani said, adding about 10 people were killed there.
"They targeted only men but I was lucky. I escaped by hiding behind the door," he said.
More top news
The police officer was shot in the arm at a petrol station on the Crumlin Road, but is in a stable condition.
Temperatures tumbling again tonight with a widespread sharp frost and lows of -5C or -6C and icy spots in places
The victim was shot in the arm in a 'drive-by' shooting.