Harris and Samia gave short statements to the media before going into a longer session of private talks.
Harris mentioned a new partnership in 5G technology and cybersecurity.
Samia said her "most important request" was to improve the visa process between the US and Tanzania.
Last November the Tanzanian president met China's President Xi Jinping during a state visit to Beijing.
Dar es Salaam
US Vice President Kamala Harris announced plans to boost trade with and investment in Tanzania during a visit there on Thursday, part of an African tour aimed at strengthening ties with a continent where China and Russia increasingly hold sway.
Harris started her trip on Sunday in Ghana before flying late on Wednesday to Tanzania's commercial capital Dar es Salaam, where she met President Samia Suluhu Hassan on Thursday.
The two women gave short statements to the media before going into a longer session of private talks.
"Working together, it is our shared goal to increase economic investment in Tanzania and strengthen our economic ties," Harris said, listing a number of initiatives.
New MoU
They included a new memorandum of understanding between the Export-Import Bank of the United States (EXIM) and the government of Tanzania.
That will facilitate up to $500 million in financing to help US companies export goods and services to Tanzania in sectors including infrastructure, transportation, digital technology, climate and energy security and power generation.
Harris also mentioned a new partnership in 5G technology and cybersecurity, as well as a US-supported plan by LifeZone Metals to open a new processing plant in Tanzania for minerals that go into electric vehicle batteries.
"This project is an important and pioneering model, using innovative and low-emission standards. Importantly, raw minerals will soon be processed in Tanzania, by Tanzanians," she said, adding that the plant would deliver battery-grade nickel to the United States and the global market from 2026.
China in Africa
China has invested heavily in Africa in the last two decades, and last November the Tanzanian president met China's President Xi Jinping during a state visit to Beijing.
Trade and investment featured heavily on their agenda, with the leaders agreeing to "elevate two-way trade and further expand the trade volume" and China saying it would explore providing market access to more Tanzanian goods.
On Thursday, President Hassan said her "most important request" was to improve the visa process between the US and Tanzania, as both countries would benefit from a "long duration visa" that would increase trade and tourism.
Magufuli isolationism
Under Hassan, Tanzania has returned to international engagement after a period of isolationism enforced by her predecessor John Pombe Magufuli, who cancelled all his ministers' foreign trips and discouraged travel.
She has won praise internationally for restoring political rights suspended by Magufuli, who died in office in 2021.
"Madam President, under your leadership Tanzania has taken important and meaningful steps and President Joe Biden and I applaud you," Harris said, standing alongside Hassan.
Magufuli had banned political rallies by anyone other than elected officials, cracked down on Tanzania's LGBT community and arrested scores of opposition supporters. He had also rejected Covid-19 vaccines and urged Tanzanians to put faith in prayer and treatments such as steam inhalation.
Reversed policies
Hassan reversed the policies upon coming to power and earlier this month, Tanzania passed the milestone of fully vaccinating 50 percent of its population against the coronavirus.
But human groups say violations continue, including government targeting of online media outlets.
Harris, the latest of several high-profile figures from the US administration to visit African countries in recent months, will Friday depart for Zambia, the final stop on her tour.