The attack at the Westgate Shopping Mall in Kenya's capital Nairobi has been greeted with outrage and an outpouring of grief by leaders who promised to stand with the country.

From New York, United Nations Secretary General Ban Ki-Moon called President Uhuru Kenyatta and expressed his solidarity with Kenyans.

“The Secretary-General is following closely and with alarm the attack on a shopping mall in Nairobi. The Secretary-General has spoken to President Uhuru Kenyatta and expressed his concern as well as offering his solidarity as the Kenyan authorities handle the incident,” he said in a statement.

Mr Ban was reported to have been receiving regular briefings from his senior advisers.

From London, British Foreign Secretary William Hague was reported to be in contact with Kenyan ministers and authorities.

“We are aware of a major security incident underway at the Westgate Shopping Centre in Nairobi. We are in close contact with the Kenyan authorities on the ground in Kenya and at ministerial level in the United Kingdom,” said Mr Hague in a brief statement.

“The prime consideration at present is the welfare of members of the public caught up in this incident,” he said

Message of solidarity

Somalia’s President Hassan Sheikh Mohamud also sent his condolences.

"We in Somalia know only too well the human costs of violence like this,” the President said. “Our prayers today are with our brothers and sisters in Kenya. We also send a strong message of solidarity with the Kenyan government, our valued partners in the campaign to bring peace to Somalia.

"These heartless acts against defenceless civilians, including innocent children, are beyond the pale and cannot be tolerated. We stand shoulder to shoulder with Kenya in its time of grief for these lives lost and the many injured.”