DAR ES SALAAM - US President Barack Obama is seeking to build a new US economic partnership with Africa as he visits Tanzania on Monday at the end of a tour of the fast-growing continent where Washington faces competition from China.

Obama's trip to Dar es Salaam occurs three months after a visit by Chinese President Xi Jinping, who came shortly after taking office. Many Africans see the US leader's three-nation tour of Africa as an attempt to play catch-up.

The US president, whose arrival was marked by a 21-gun salute, meets his predecessor, George W. Bush, who is also visiting. They will join a ceremony on Tuesday to lay a wreath to those killed in the 1998 US embassy bombing in Tanzania.

Apparently trying to regain ground, Washington plans a $7 billion initiative to help tackle Africa's crippling lack of electrical power. On Tuesday, Obama visits an independent power plan in Tanzania run since 2011 by US-based Symbion.

The White House said Obama would launch a project in Tanzania, called Trade Africa, on Monday, initially focusing on an east African trade bloc that has a combined population of 130 million people. It would later be expanded, the statement added.

Although growing quickly, economists said Tanzania's economy could expand faster with reliable power and more internal trade.

Tanzanian businesses often complain of the expense of running standby generators and other related costs.

"Electricity supply is very erratic," Susan Maganga, who runs a hair salon in Dar es Salaam, said as Obama arrived in the commercial capital. "I have to buy petrol for a power generator almost on a daily basis, which is a major drain on my business."

It is a grumble heard across Africa, including in neighbouring Kenya, the homeland of Obama's father.

Many Kenyans were upset that Obama chose Tanzania and not Kenya, east Africa's biggest economy, for his third stop.

Explaining his decision, Obama said it was not the "optimal time" to travel to Nairobi when the new Kenyan administration was dealing with cases at the International Criminal Court in the Hague. He also said he could do so later in his term.

President Uhuru Kenyatta and his deputy, William Ruto, elected in March, both face charges of crimes against humanity for their alleged roles in post-election violence five years ago. Kenyatta's case starts in November.

During Kenya's campaign, then-US Assistant Secretary of State for African Affairs Johnnie Carson told voters "choices have consequences", riling many who saw his remarks as aimed at discouraging a vote for Kenyatta. Some Kenyan media commentators have said Obama's decision not to visit is one such consequence.