Wall Street stocks were under pressure for a third straight session on Thursday after digesting mixed economic data while it looks ahead to a key labour market report.

Stocks "struggled to get traction ahead of a very important jobs report tomorrow," said Angelo Kourkafas of Edward Jones. "Investors are cautious of taking on more risk given the market's sensitivity of what we might learn tomorrow."

Friday's Department of Labour data comes as other data suggest a US economy that is slowing but not necessarily heading into a recession; a weak jobs report could challenge that view.

Analysts have estimated that Friday's jobs data will show the US economy added 165,000 jobs while unemployment will dip slightly to 4.2 percent.

The Dow Jones finished Thursday down 0.5 percent at 40,755.

The S&P 500 declined 0.3 percent to 5,503, while the Nasdaq gained 0.3 percent to 17,127.

Data released on Thursday from payroll firm ADP showed private sector employment rose by 99,000 in August, well below the 150,000 estimated by analysts.

Meanwhile the Institute for Supply Management's services index crept up to 51.5 percent last month from 51.4 percent in July, slightly topping estimates.

Among individual companies, Frontier Communications Parent fell 9.5 percent on Thursday after agreeing to be acquired by Verizon for US$20 billion.

Verizon, which said Frontier's fibre internet assets will enhance its broadband capacity, dipped 0.4 percent.

Tesla jumped 4.9 percent after announcing plans to launch its "full self-driving" technology in Europe and China early next year, pending regulatory approval.

JetBlue advanced 7.2 percent as it lifted its third-quarter revenue target, citing strong bookings, particularly in the Latin America region, and a boost due to rebookings from a rival carrier that experienced technology outages. (AFP)