Trading on the New Zealand sharemarket was halted for nearly an hour late in the afternoon, but it had still done enough work to surge closer to its all-time high.

The stock exchange experienced a network outage within the Wellington and Auckland data centre, the NZX website was down and trading stopped just before 4pm. An hour later the S&P/NZX 50 Index emerged at 11,993.18 points, up 72.10 points or 0.6 per cent.

"NZX's network service provider encountered an issue this afternoon which impacted NZX system connectivity. As such, NZX decided to halt trading in its cash markets at approximately 15.57. NZX's network provider continues to investigate the source of the issue," the NZX said late afternoon.

Wealth manager Jarden advised clients "this is currently impacting external parties connecting to NZX via the internet eg: VPN and nzx.com. As result asymmetric access to NZX has suspended NZSX (Cash markets) until network connectivity can be restored."

During the disrupted day the index reached a high of 12,003.47 points, just 70 points away from the record 12,073.34 achieved on February 21 this year.

There were 111 gainers and 36 decliners over the whole market, and 42.6 million shares worth $165.04 million were traded.

Jeremy Sullivan, investment adviser with Hamilton Hindin Greene, said "we had another positive trading day and the market is climbing ever closer to the all-time high. Investors are confident with the reporting season being by and large better than expected in March and April, and there is optimism around the timeframe of Auckland getting out of level 3 lockdown."

The market was also buoyed by another strong day on Wall Street, with S&P 500 Index, up 1 per cent to 3431.28 points, and the Nasdaq, up 0.6 per cent to 11,379.72 points, hitting new record levels. The Dow Jones Industrial Index increased 1.35 per cent to 28,308.46.

The United States markets reacted to positive developments over a coronavirus treatment, with the Food and Drug Administration granting emergency authorisation for a Covid-19 plasma procedure. The number of United States infections also declined.

Many of the New Zealand market heavyweights had strong gains, even though a2 Milk fell 40c to $20.03. Fisher and Paykel Healthcare was up 53c to $36.28; Mainfreight climbed 76c to $47.01; Spark increased 11c to $5.03; Meridian was up 12c to $5.12; Mercury gained 16.5 to $5.225; and Contact Energy was up 10c to $6.46.

After producing a solid result, analysts upgraded Chorus and its share price finished at $8.545, up 34c or 4.1 per cent. Freightways increased 20c to $7.30 following its financial result.

Napier Port reported slightly lower revenue and underlying earnings for the nine months ending June after the Covid disruptions affected container volume, down 2.9 per cent, and bulk cargo, down 12.8 per cent.

Its revenue fell 1.4 per cent to $76.6m but net profit increased from $16.3m to $18.7m, and Napier Port's share price rose 6c or 1.7 per cent to $3.54. The port is now expecting its full-year profit will be about $20m.

Media company NZME soared 13c or 44.8 per cent to 42c after showing an improvement in business. NZME's operating earnings (ebitda) increased 5 per cent to $28.9m, from $27.6m, for the six months ending June.

Revenue fell 13 per cent to $157.8m, from $181m, while net profit improved to $3m compared with $0.9m the same period last year. NZ Herald Premium had 82,000 digital subscribers generating revenue of $2.4m, and OneRoof holds more than 83 per cent of residential listings in New Zealand, producing $1.4m of digital classified revenue.

Transport Technology company EROAD climbed 15c or 3.7 per cent to $4.20 after extending an American contract. Mercer Group is changing its name to MHM Automation on September 1, reflecting its specialised automation solutions business, and its share price rose 5.5c or 20.8 per cent to 32c.

- Additional reporting Hamish Rutherford