Chittagong, Mar 1: Graeme Smith and Neil McKenzie broke the world record for the highest opening stand as the South African run juggernaut continued to roll in the second Test against Bangladesh here today.

At lunch on the second day of the match at the Chittagong Divisional stadium, South Africa were 509-1 with Neil McKenzie going strong on 223 and Hashim Amla unbeaten on 35.

Resuming the day at 405-0 and with just nine needed to break the 52-year-old world record, the South African openers reached the milestone when Smith took a single past square leg off Shakib Al Hasan.

The earlier record stood in the name of India's Vinoo Mankad and Pankaj Roy who put on 413 against New Zealand in Chennai in 1956.

The mammoth stand came to an end balls and two runs later when Smith (232) was bowled by Abdur Razzaq while trying to sweep a flighted delivery from the left-arm spinner.

Smith, who slammed 33 fours and a six in his aggressive 277-ball knock, also became the first South African to score four Test double-centuries, surpassing Herschelle Gibbs (3).

McKenzie, meanwhile, continued to punish the luckless Bangladesh bowlers, having hit 28 fours and three sixes so far in his career-best knock. He has so far faced 382 balls during his marathon 509-minute stay at the wicket.

This was only the second instance ever of both openers making double centuries in an innings. Australia's Bill Lawry and Bobby Simpson had achieved the feat for the first time against West Indies at Bridgetown in 1964-65.

Amla too appeared to be getting into a groove on a wicket that continued to frustrate the home team bowlers.

South Africa lead the two-Test series 1-0 after winning the opener in Dhaka by five wickets.