NAIROBI - A lunch-hour blast at a clothes shop in Kenya's capital Nairobi on Monday caused panic and disrupted activities in the central business district, while the government is calling for cooperation in the East African country's relentless fight against terror.

Business in Nairobi, East Africa's business hub, was thrown into disarray as people rushed to the scene of the blast to try and help victims.

Others abandoned their undertaking to get information on the explosion that shook the city and its people.

Pandemonium prevailed in the heart of the capital as a huge smoke, which could be spotted from far, billowed from the scene of the blast into the sky.

Most employees, who had left their offices for lunch in various eateries, delayed returning to their workplaces as they went to Moi Avenue, the scene of the explosion.

"We were having lunch at a restaurant on Tom Mboya Street, which is separated by buildings from the scene of the blast when the explosion happened. We left our food and rushed out of the restaurant fearing for our lives," said Bernard Mumia.

The insurance agent said there was a lot of confusion on the streets as people wanted to know what had happened. "People were running all over. There was a lot of confusion as we headed to the scene of the blast," he recounted.

At the scene, he said a huge fire had engulfed the building and people were being evacuated from adjacent buildings.

"I saw a man whose shirt was drained in blood running from one of the building seeking help. He was helped into an ambulance that had just arrived," he said.

And as rescue efforts went on, traffic within the city center was disrupted as Moi Avenue and adjacent roads were closed. Traffic had already built up before the effect of the blast took a toll on Nairobi.

Ambulances and fire brigade vehicles had to wade through massive traffic jams, which had build up as peak hour beckoned.

"I saw two ambulances racing towards town but I did not know exactly what was wrong. It was later that I heard on radio there was blast in the city center," said Ambrose Muriuki, who was driving to the city center.

Muriuki lamented that the traffic jams hampered rescue efforts. "Traffic jams in Nairobi are a curse. This comes to the fore in times of disaster. Movement of rescue vehicles becomes a problem. Today, it was no different because of the snarl-ups," he said.

Most owners of stalls, especially on Tom Mboya Street and Moi Avenue, which host dozens of small shops, shut them for some hours.

There was panic as traders shut the shops and conducted searches to find out if there were any explosives.

"We were trying to ensure our businesses are safe. This is because the shop that was hit by a blast was a stall. Terrorists my have tried to set up simultaneous attacks," said Beatrice Kiarie, who was called by her employee and told her to shut the stall located on Tom Mboya Street.

She added that they suspected looters could have taken advantage of the confusion and attacked them.

The blast brought back memories of the 1997 bomb attack in Nairobi when Al-Qaida operatives attacked the city and killed several people and injured hundred others.

It is not clear what was the cause of Monday's blast but Police Commissioner Mathew Iteere blamed it on an electric fault resulting from an underground transformer.

"The blast could be as a result of an electric fault but not a grenade or bomb blast since injuries of victims do not show they were caused by the two," he said.

However, Kenya Power has since dismissed the claims noting that the building did not have an underground transformer.

"The building has no transformer mounted inside it or outside that would have exploded. Our technicians have ascertained all power installations were intact," Kenya Power said in a statement.

Kenyan Prime Minister Raila Odinga termed the blast an act of terrorism. "This is a cowardly act that should be condemned. I urge all Kenyans to support our security forces as they work hard to eliminate acts of terrorism."

According to police and Kenya Red Cross, at least 30 people were injured in the blast, four of them critically.